diff --git a/lib/mongo/collection.rb b/lib/mongo/collection.rb
index c0e057c..e68a1fc 100644
--- a/lib/mongo/collection.rb
+++ b/lib/mongo/collection.rb
@@ -74,6 +74,8 @@ module Mongo
       @db, @name  = db, name
       @connection = @db.connection
       @logger     = @connection.logger
+      @cache_time = @db.cache_time
+      @cache = Hash.new(0)
       unless pk_factory
         @safe       = options.has_key?(:safe) ? options[:safe] : @db.safe
       end
@@ -407,53 +409,48 @@ module Mongo
     # @core indexes create_index-instance_method
     def create_index(spec, opts={})
       opts[:dropDups] = opts.delete(:drop_dups) if opts[:drop_dups]
-      field_spec = BSON::OrderedHash.new
-      if spec.is_a?(String) || spec.is_a?(Symbol)
-        field_spec[spec.to_s] = 1
-      elsif spec.is_a?(Array) && spec.all? {|field| field.is_a?(Array) }
-        spec.each do |f|
-          if [Mongo::ASCENDING, Mongo::DESCENDING, Mongo::GEO2D].include?(f[1])
-            field_spec[f[0].to_s] = f[1]
-          else
-            raise MongoArgumentError, "Invalid index field #{f[1].inspect}; " + 
-              "should be one of Mongo::ASCENDING (1), Mongo::DESCENDING (-1) or Mongo::GEO2D ('2d')."
-          end
-        end
-      else
-        raise MongoArgumentError, "Invalid index specification #{spec.inspect}; " + 
-          "should be either a string, symbol, or an array of arrays."
-      end
-
+      field_spec = parse_index_spec(spec)
       name = opts.delete(:name) || generate_index_name(field_spec)
-
-      selector = {
-        :name   => name,
-        :ns     => "#{@db.name}.#{@name}",
-        :key    => field_spec
-      }
-      selector.merge!(opts)
-
-      begin
-      insert_documents([selector], Mongo::DB::SYSTEM_INDEX_COLLECTION, false, true)
-
-      rescue Mongo::OperationFailure => e
-        if selector[:dropDups] && e.message =~ /^11000/
-          # NOP. If the user is intentionally dropping dups, we can ignore duplicate key errors.
-        else
-          raise Mongo::OperationFailure, "Failed to create index #{selector.inspect} with the following error: " +
-           "#{e.message}"
-        end
-      end
-
+      
+      generate_indexes(field_spec, name, opts)
       name
     end
 
+    
+    # Calls create_index and sets a flag to not do so again for another X minutes.
+    # this time can be specified as an option when initializing a Mongo::Db object as options[:cache_time]
+    # Any changes to an index will be propogated through regardless of cache time (eg, if you change index direction)
+    # @example Call sequence:
+    #   Time t: @posts.ensure_index([['subject', Mongo::ASCENDING])  -- calls create_index and sets the 5 minute cache
+    #   Time t+2min : @posts.ensure_index([['subject', Mongo::ASCENDING])  -- doesn't do anything
+    #   Time t+3min : @posts.ensure_index([['something_else', Mongo::ASCENDING])  -- calls create_index and sets 5 minute cache
+    #   Time t+10min : @posts.ensure_index([['subject', Mongo::ASCENDING])  -- calls create_index and resets the 5 minute counter
+    def ensure_index(spec, opts={})
+      valid = BSON::OrderedHash.new
+      now = Time.now.utc.to_i
+      field_spec = parse_index_spec(spec)
+
+            
+      field_spec.each do |key, value|
+        cache_key = generate_index_name({key => value}) #bit of a hack.
+        timeout = @cache[cache_key] || 0
+        valid[key] = value if timeout <= now
+      end
+      name = opts.delete(:name) || generate_index_name(valid)
+      generate_indexes(valid, name, opts) if valid.any?
+      
+      # I do this here instead of in the above loop in case there were any errors inserting. Best to be safe.
+      name.each {|n| @cache[n] = now + @cache_time}
+      name
+    end
+    
     # Drop a specified index.
     #
     # @param [String] name
     #
     # @core indexes
     def drop_index(name)
+      @cache[name] = [] # I do this first because there is no harm in clearing the cache.
       @db.drop_index(@name, name)
     end
 
@@ -461,7 +458,7 @@ module Mongo
     #
     # @core indexes
     def drop_indexes
-
+      @cache = {}
       # Note: calling drop_indexes with no args will drop them all.
       @db.drop_index(@name, '*')
     end
@@ -712,6 +709,51 @@ module Mongo
     end
 
     private
+    
+    
+    def parse_index_spec(spec)
+      field_spec = BSON::OrderedHash.new
+      if spec.is_a?(String) || spec.is_a?(Symbol)
+        field_spec[spec.to_s] = 1
+      elsif spec.is_a?(Array) && spec.all? {|field| field.is_a?(Array) }
+        spec.each do |f|
+          if [Mongo::ASCENDING, Mongo::DESCENDING, Mongo::GEO2D].include?(f[1])
+            field_spec[f[0].to_s] = f[1]
+          else
+            raise MongoArgumentError, "Invalid index field #{f[1].inspect}; " + 
+              "should be one of Mongo::ASCENDING (1), Mongo::DESCENDING (-1) or Mongo::GEO2D ('2d')."
+          end
+        end
+      else
+        raise MongoArgumentError, "Invalid index specification #{spec.inspect}; " + 
+          "should be either a string, symbol, or an array of arrays."
+      end
+      field_spec
+    end
+    
+    def generate_indexes(field_spec, name, opts)
+      selector = {
+        :name   => name,
+        :ns     => "#{@db.name}.#{@name}",
+        :key    => field_spec
+      }
+      selector.merge!(opts)
+
+      begin
+      insert_documents([selector], Mongo::DB::SYSTEM_INDEX_COLLECTION, false, true)
+
+      rescue Mongo::OperationFailure => e
+        if selector[:dropDups] && e.message =~ /^11000/
+          # NOP. If the user is intentionally dropping dups, we can ignore duplicate key errors.
+        else
+          raise Mongo::OperationFailure, "Failed to create index #{selector.inspect} with the following error: " +
+           "#{e.message}"
+        end
+      end
+
+      nil
+    end
+    
 
     # Sends a Mongo::Constants::OP_INSERT message to the database.
     # Takes an array of +documents+, an optional +collection_name+, and a
diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index db219c6..cd19d0f 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -51,6 +51,9 @@ module Mongo
     # The Mongo::Connection instance connecting to the MongoDB server.
     attr_reader :connection
 
+    # The length of time that Collection.ensure_index should cache index calls
+    attr_accessor :cache_time
+
     # Instances of DB are normally obtained by calling Mongo#db.
     #
     # @param [String] db_name the database name.
@@ -70,6 +73,7 @@ module Mongo
     #   value is provided, the default value set on this instance's Connection object will be used. This
     #   default can be overridden upon instantiation of any collection by explicity setting a :safe value
     #   on initialization
+    # @option options [Integer] :cache_time (300) Set the time that all ensure_index calls should cache the command.
     #
     # @core databases constructor_details
     def initialize(db_name, connection, options={})
@@ -78,6 +82,7 @@ module Mongo
       @strict     = options[:strict]
       @pk_factory = options[:pk]
       @safe       = options.has_key?(:safe) ? options[:safe] : @connection.safe
+      @cache_time = options[:cache_time] || 300 #5 minutes.
     end
 
     # Authenticate with the given username and password. Note that mongod
diff --git a/test/collection_test.rb b/test/collection_test.rb
index b7acd00..e6842dc 100644
--- a/test/collection_test.rb
+++ b/test/collection_test.rb
@@ -565,6 +565,30 @@ class TestCollection < Test::Unit::TestCase
 
     assert_equal 1, x
   end
+  
+  
+  def test_ensure_index
+    @@test.drop_indexes
+    @@test.insert("x" => "hello world")
+    assert_equal 1, @@test.index_information.keys.count #default index
+    
+    @@test.ensure_index([["x", Mongo::DESCENDING]], {})
+    assert_equal 2, @@test.index_information.keys.count
+    assert @@test.index_information.keys.include? "x_-1"
+    
+    @@test.ensure_index([["x", Mongo::ASCENDING]])
+    assert @@test.index_information.keys.include? "x_1"
+    
+    @@test.drop_index("x_1")
+    assert_equal 2, @@test.index_information.keys.count
+    @@test.drop_index("x_-1")
+    assert_equal 1, @@test.index_information.keys.count
+    
+    @@test.ensure_index([["x", Mongo::DESCENDING]], {}) #should work as not cached.
+    assert_equal 2, @@test.index_information.keys.count
+    assert @@test.index_information.keys.include? "x_-1"
+    
+  end
 
   context "Grouping" do
     setup do
diff --git a/test/unit/collection_test.rb b/test/unit/collection_test.rb
index 8907ad6..3c899c9 100644
--- a/test/unit/collection_test.rb
+++ b/test/unit/collection_test.rb
@@ -81,5 +81,54 @@ class CollectionTest < Test::Unit::TestCase
       @logger.stubs(:debug)
       @coll.update({}, {:title => 'Moby Dick'}, :safe => true)
     end
+    
+    should "not call insert for each ensure_index call" do
+      @conn = Connection.new('localhost', 27017, :logger => @logger, :connect => false)
+      @db   = @conn['testing']
+      @coll = @db.collection('books')
+      @coll.expects(:generate_indexes).once
+      
+      @coll.ensure_index [["x", Mongo::DESCENDING]]
+      @coll.ensure_index [["x", Mongo::DESCENDING]]
+      
+    end
+    should "call generate_indexes for a new direction on the same field for ensure_index" do
+      @conn = Connection.new('localhost', 27017, :logger => @logger, :connect => false)
+      @db   = @conn['testing']
+      @coll = @db.collection('books')
+      @coll.expects(:generate_indexes).twice
+      
+      @coll.ensure_index [["x", Mongo::DESCENDING]]
+      @coll.ensure_index [["x", Mongo::ASCENDING]]
+      
+    end
+    
+    should "call generate_indexes twice because the cache time is 0 seconds" do
+      @conn = Connection.new('localhost', 27017, :logger => @logger, :connect => false)
+      @db   = @conn['testing']
+      @db.cache_time = 0
+      @coll = @db.collection('books')
+      @coll.expects(:generate_indexes).twice
+      
+
+      @coll.ensure_index [["x", Mongo::DESCENDING]]
+      @coll.ensure_index [["x", Mongo::DESCENDING]]
+      
+    end
+    
+    should "call generate_indexes for each key when calling ensure_indexes" do
+      @conn = Connection.new('localhost', 27017, :logger => @logger, :connect => false)
+      @db   = @conn['testing']
+      @db.cache_time = 300
+      @coll = @db.collection('books')
+      @coll.expects(:generate_indexes).once.with do |a, b, c|
+        a == {"x"=>-1, "y"=>-1}
+      end
+      
+      @coll.ensure_index [["x", Mongo::DESCENDING], ["y", Mongo::DESCENDING]]
+    end
+
+    
+    
   end
 end