diff --git a/README.md b/README.md
index 088dff4..8393563 100644
--- a/README.md
+++ b/README.md
@@ -55,7 +55,12 @@ factory_girl_rails is available in the development group. If it's not, Rails
 will generate standard .yml files instead of factory files.
 
 factory_girl takes an option `suffix: 'some_suffix'` to generate factories as
-`modelname_some_suffix.rb`.
+1modelname_some_suffix.rb`.
+
+If you use factory_girl for fixture replacement and already have a
+`factories.rb` file in the directory that contains your tests,
+factory_girl_rails will insert new factory definitions at the top of
+`factories.rb`.
 
 ## Contributing
 
diff --git a/features/generators.feature b/features/generators.feature
index 446795a..547b02b 100644
--- a/features/generators.feature
+++ b/features/generators.feature
@@ -8,7 +8,7 @@ Feature:
     And I cd to "testapp"
     And I add "factory_girl_rails" from this project as a dependency
 
-  Scenario: The factory_girl_rails generators create a factory file for each model that I generate
+  Scenario: The factory_girl_rails generators create a factory file for each model if there is not a factories.rb file
     When I run `bundle install` with a clean environment
     And I run `bundle exec rails generate model User name:string --fixture-replacement=factory_girl` with a clean environment
     And I run `bundle exec rails generate model Namespaced::User name:string --fixture-replacement=factory_girl` with a clean environment
@@ -17,12 +17,12 @@ Feature:
     And the file "test/factories/users.rb" should contain "factory :user do"
     And the file "test/factories/namespaced_users.rb" should contain "factory :namespaced_user, :class => 'Namespaced::User' do"
 
-  Scenario: The factory_girl_rails generators create a factory file with a custom name for each model that I generate
+  Scenario: The factory_girl_rails generators does not create a factory file for each model if there is a factories.rb file in the test directory
     When I run `bundle install` with a clean environment
-    And I set the FactoryGirl :suffix option to "factory"
+    And I write to "test/factories.rb" with:
+      """
+      FactoryGirl.define do
+      end
+      """
     And I run `bundle exec rails generate model User name:string --fixture-replacement=factory_girl` with a clean environment
-    And I run `bundle exec rails generate model Namespaced::User name:string --fixture-replacement=factory_girl` with a clean environment
-    Then the output should contain "test/factories/users_factory.rb"
-    And the output should contain "test/factories/namespaced_users_factory.rb"
-    And the file "test/factories/users_factory.rb" should contain "factory :user do"
-    And the file "test/factories/namespaced_users_factory.rb" should contain "factory :namespaced_user, :class => 'Namespaced::User' do"
+    Then the file "test/factories.rb" should contain "factory :user do"
diff --git a/lib/generators/factory_girl/model/model_generator.rb b/lib/generators/factory_girl/model/model_generator.rb
index d01cbcb..21d6bca 100644
--- a/lib/generators/factory_girl/model/model_generator.rb
+++ b/lib/generators/factory_girl/model/model_generator.rb
@@ -4,28 +4,82 @@ require 'factory_girl_rails'
 module FactoryGirl
   module Generators
     class ModelGenerator < Base
-      argument :attributes, :type => :array, :default => [], :banner => "field:type field:type"
-      class_option :dir, :type => :string, :default => "test/factories", :desc => "The directory where the factories should go"
+      argument(
+        :attributes,
+        type: :array,
+        default: [],
+        banner: "field:type field:type"
+      )
+
+      class_option(
+        :dir,
+        type: :string,
+        default: "test/factories",
+        desc: "The directory or file root where factories belong"
+      )
 
       def create_fixture_file
-        filename = [table_name, filename_suffix].compact.join('_')
-        template 'fixtures.erb', File.join(options[:dir], "#{filename}.rb")
+        if File.exist?(factories_file)
+          insert_factory_into_existing_file
+        else
+          create_factory_file
+        end
       end
 
       private
 
+      def factories_file
+        options[:dir] + ".rb"
+      end
+
+      def insert_factory_into_existing_file
+        insert_into_file(
+          factories_file,
+          factory_definition,
+          after: "FactoryGirl.define do"
+        )
+      end
+
+      def create_factory_file
+        filename = [table_name, filename_suffix].compact.join('_')
+        file = File.join(options[:dir], "#{filename}.rb")
+        create_file(file, single_file_factory_definition)
+      end
+
+      def factory_definition
+<<-RUBY
+  factory :#{singular_table_name}#{explicit_class_option} do
+    #{factory_attributes}
+  end
+RUBY
+      end
+
+      def single_file_factory_definition
+<<-RUBY
+FactoryGirl.define do
+#{factory_definition}
+end
+RUBY
+      end
+
+      def factory_attributes
+        attributes.map do |attribute|
+          "#{attribute.name} #{attribute.default.inspect}"
+        end.join("\n")
+      end
+
       def filename_suffix
         factory_girl_options[:suffix]
       end
 
+      def factory_girl_options
+        generators.options[:factory_girl] || {}
+      end
+
       def generators
         config = FactoryGirl::Railtie.config
         config.respond_to?(:app_generators) ? config.app_generators : config.generators
       end
-
-      def factory_girl_options
-        generators.options[:factory_girl] || {}
-      end
     end
   end
 end
diff --git a/lib/generators/factory_girl/model/templates/fixtures.erb b/lib/generators/factory_girl/model/templates/fixtures.erb
deleted file mode 100644
index 71d7da4..0000000
--- a/lib/generators/factory_girl/model/templates/fixtures.erb
+++ /dev/null
@@ -1,9 +0,0 @@
-# Read about factories at https://github.com/thoughtbot/factory_girl
-
-FactoryGirl.define do
-  factory :<%= singular_table_name %><%= explicit_class_option %> do
-<% for attribute in attributes -%>
-    <%= attribute.name %> <%= attribute.default.inspect %>
-<% end -%>
-  end
-end