diff --git a/bin/_mocha b/bin/_mocha
index 0086568523..dc0e82bf1b 100755
--- a/bin/_mocha
+++ b/bin/_mocha
@@ -258,11 +258,11 @@ mocha.suite.bail(program.bail);
 
 // --grep
 
-if (program.grep) mocha.grep(new RegExp(program.grep));
+if (program.grep) mocha.grep(program.grep);
 
 // --fgrep
 
-if (program.fgrep) mocha.grep(program.fgrep);
+if (program.fgrep) mocha.fgrep(program.fgrep);
 
 // --invert
 
diff --git a/lib/mocha.js b/lib/mocha.js
index 1817ccf2c6..4799377654 100644
--- a/lib/mocha.js
+++ b/lib/mocha.js
@@ -79,7 +79,7 @@ function Mocha(options) {
     this.grep(new RegExp(options.grep));
   }
   if (options.fgrep) {
-    this.grep(options.fgrep);
+    this.fgrep(options.fgrep);
   }
   this.suite = new exports.Suite('', new exports.Context());
   this.ui(options.ui);
@@ -240,6 +240,17 @@ Mocha.prototype._growl = function(runner, reporter) {
   });
 };
 
+/**
+ * Escape string and add it to grep as a regexp.
+ *
+ * @api public
+ * @param str
+ * @returns {Mocha}
+ */
+Mocha.prototype.fgrep = function(str) {
+  return this.grep(new RegExp(escapeRe(str)));
+};
+
 /**
  * Add regexp to grep, if `re` is a string it is escaped.
  *
@@ -248,10 +259,15 @@ Mocha.prototype._growl = function(runner, reporter) {
  * @return {Mocha}
  */
 Mocha.prototype.grep = function(re) {
-  this.options.grep = typeof re === 'string' ? new RegExp(escapeRe(re)) : re;
+  if (utils.isString(re)) {
+    // extract args if it's regex-like, i.e: [string, pattern, flag]
+    var arg = re.match(/^\/(.*)\/(g|i|)$|.*/);
+    this.options.grep = new RegExp(arg[1] || arg[0], arg[2]);
+  } else {
+    this.options.grep = re;
+  }
   return this;
 };
-
 /**
  * Invert `.grep()` matches.
  *
diff --git a/support/browser-entry.js b/support/browser-entry.js
index 7655807fae..5bd93af4c2 100644
--- a/support/browser-entry.js
+++ b/support/browser-entry.js
@@ -126,8 +126,8 @@ mocha.run = function(fn){
   mocha.globals('location');
 
   var query = Mocha.utils.parseQuery(global.location.search || '');
-  if (query.grep) mocha.grep(new RegExp(query.grep));
-  if (query.fgrep) mocha.grep(query.fgrep);
+  if (query.grep) mocha.grep(query.grep);
+  if (query.fgrep) mocha.fgrep(query.fgrep);
   if (query.invert) mocha.invert();
 
   return Mocha.prototype.run.call(mocha, function(err){
diff --git a/test/grep.js b/test/grep.js
index 633aab4e63..bbc5c55eba 100644
--- a/test/grep.js
+++ b/test/grep.js
@@ -5,44 +5,61 @@ describe('Mocha', function(){
     it('should add a RegExp to the mocha.options object', function(){
       var mocha = new Mocha({ grep: /foo.*/ });
       mocha.options.grep.toString().should.equal('/foo.*/');
-    })
+    });
 
     it('should convert string to a RegExp', function(){
       var mocha = new Mocha({ grep: 'foo.*' });
       mocha.options.grep.toString().should.equal('/foo.*/');
-    })
-  })
+    });
+  });
 
   describe('"fgrep" option', function(){
     it('should escape and convert string to a RegExp', function(){
       var mocha = new Mocha({ fgrep: 'foo.*' });
       mocha.options.grep.toString().should.equal('/foo\\.\\*/');
-    })
-  })
+    });
+  });
 
-  describe('.grep()', function(){
-    it('should add a RegExp to the mocha.options object', function(){
-      var mocha = new Mocha;
-      mocha.grep(/foo/);
-      mocha.options.grep.toString().should.equal('/foo/');
-    })
+  describe('.grep()', function() {
+    // Test helper
+    function testGrep(mocha) {
+      return function testGrep(grep, expected) {
+        mocha.grep(grep);
+        mocha.options.grep.toString().should.equal(expected);
+      }
+    }
 
-    it('should convert grep string to a RegExp', function(){
-      var mocha = new Mocha;
-      mocha.grep('foo');
-      mocha.options.grep.toString().should.equal('/foo/');
-    })
+    it('should add a RegExp to the mocha.options object', function() {
+      var test = testGrep(new Mocha);
+      test(/foo/, '/foo/');
+    });
+
+    it('should convert grep string to a RegExp', function() {
+      var test = testGrep(new Mocha);
+      test('foo', '/foo/');
+      test('^foo.*bar$', '/^foo.*bar$/');
+      test('^@.*(?=\\(\\)$)', '/^@.*(?=\\(\\)$)/');
+    });
+
+    it('should covert grep regex-like string to a RegExp', function() {
+      var test = testGrep(new Mocha);
+      test('/foo/', '/foo/');
+      // Keep the flags
+      test('/baz/i', '/baz/i');
+      test('/bar/g', '/bar/g');
+      test('/^foo(.*)bar/g', '/^foo(.*)bar/g');
+    });
 
     it('should return it\'s parent Mocha object for chainability', function(){
       var mocha = new Mocha;
       mocha.grep().should.equal(mocha);
-    })
-  })
+    });
+  });
 
   describe('"invert" option', function(){
     it('should add a Boolean to the mocha.options object', function(){
       var mocha = new Mocha({ invert: true });
       mocha.options.invert.should.be.ok;
-    })
-  })
-})
+    });
+  });
+});
diff --git a/test/integration/fixtures/options/grep.js b/test/integration/fixtures/options/grep.js
index 5e163f5ee7..94785dc7db 100644
--- a/test/integration/fixtures/options/grep.js
+++ b/test/integration/fixtures/options/grep.js
@@ -1,10 +1,15 @@
 describe('grep', function() {
+  describe('Match', function() {
+    it('should run', function(){});
+    it('should also run', function() {});
+  });
+
   describe('match', function() {
     it('should run', function(){});
     it('should also run', function() {});
   });
 
-  describe('fail', function(){
+  describe('fail', function() {
     it('should not be ran', function() {
       throw new Error('Spec should not run');
     });
diff --git a/test/integration/options.js b/test/integration/options.js
index db3710913b..d4a32a03fe 100644
--- a/test/integration/options.js
+++ b/test/integration/options.js
@@ -111,15 +111,29 @@ describe('options', function() {
       });
     });
 
-    it('runs specs matching a RegExp', function(done) {
-      args = ['--grep', '.*'];
-      run('options/grep.js', args, function(err, res) {
-        assert(!err);
-        assert.equal(res.stats.pending, 0);
-        assert.equal(res.stats.passes, 2);
-        assert.equal(res.stats.failures, 1);
-        assert.equal(res.code, 1);
-        done();
+    describe('runs specs matching a RegExp', function() {
+      it('with RegExp like strings(pattern follow by flag)', function(done) {
+        args = ['--grep', '/match/i'];
+        run('options/grep.js', args, function(err, res) {
+          assert(!err);
+          assert.equal(res.stats.pending, 0);
+          assert.equal(res.stats.passes, 4);
+          assert.equal(res.stats.failures, 0);
+          assert.equal(res.code, 0);
+          done();
+        });
+      });
+
+      it('string as pattern', function(done) {
+        args = ['--grep', '.*'];
+        run('options/grep.js', args, function(err, res) {
+          assert(!err);
+          assert.equal(res.stats.pending, 0);
+          assert.equal(res.stats.passes, 4);
+          assert.equal(res.stats.failures, 1);
+          assert.equal(res.code, 1);
+          done();
+        });
       });
     });
 
@@ -129,7 +143,7 @@ describe('options', function() {
         run('options/grep.js', args, function(err, res) {
           assert(!err);
           assert.equal(res.stats.pending, 0);
-          assert.equal(res.stats.passes, 2);
+          assert.equal(res.stats.passes, 4);
           assert.equal(res.stats.failures, 0);
           assert.equal(res.code, 0);
           done();