diff --git a/README.md b/README.md
index 3eed30a..661a208 100644
--- a/README.md
+++ b/README.md
@@ -167,6 +167,7 @@ components following the same API.
 ### Validators
 
 * matchField
+* requiresFieldIfEmpty
 * min
 * max
 * range
diff --git a/example/complex.js b/example/complex.js
index 53050e3..9b17f68 100644
--- a/example/complex.js
+++ b/example/complex.js
@@ -31,6 +31,12 @@ var form = forms.create({
         required: true,
         validators: [validators.matchField('password')]
     }),
+    phone_1: fields.string({
+        validators: [validators.requiresFieldIfEmpty('phone_2')]
+    }),
+    phone_2: fields.string({
+        validators: [validators.requiresFieldIfEmpty('phone_1')]
+    }),
     options: fields.string({
         choices: {
             one: 'option one',
diff --git a/lib/fields.js b/lib/fields.js
index 14858c6..28f91a9 100644
--- a/lib/fields.js
+++ b/lib/fields.js
@@ -33,7 +33,10 @@ exports.string = function (opt) {
         b.value = raw_data;
         b.data = b.parse(raw_data);
         b.validate = function (form, callback) {
-            if (raw_data === '' || raw_data === null || typeof raw_data === 'undefined') {
+            var forceValidation = (b.validators || []).some(function (validator) {
+                return validator.forceValidation;
+            });
+            if (!forceValidation && (raw_data === '' || raw_data === null || typeof raw_data === 'undefined')) {
                 // don't validate empty fields, but check if required
                 if (b.required) { b.error = 'This field is required.'; }
                 process.nextTick(function () { callback(null, b); });
diff --git a/lib/validators.js b/lib/validators.js
index d8caf18..0bbe836 100644
--- a/lib/validators.js
+++ b/lib/validators.js
@@ -1,7 +1,23 @@
 /*jslint node: true */
 'use strict';
 
-var util  = require('util');
+var util = require('util');
+
+// From https://github.com/kriskowal/es5-shim/blob/master/es5-shim.js#L1238-L1257
+var trim = (function () {
+    var ws = "\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF",
+        wsChars = '[' + ws + ']',
+        trimBeginRegexp = new RegExp("^" + wsChars + wsChars + "*"),
+        trimEndRegexp = new RegExp(wsChars + wsChars + "*$");
+    return function (str) {
+        str = str ? String(str) : '';
+        if (String.prototype.trim && !ws.trim()) {
+            return str.trim();
+        } else {
+            return String(this).replace(trimBeginRegexp, '').replace(trimEndRegexp, '');
+        };
+    }
+}());
 
 exports.matchField = function (match_field, message) {
     if (!message) { message = 'Does not match %s.'; }
@@ -14,6 +30,21 @@ exports.matchField = function (match_field, message) {
     };
 };
 
+exports.requiresFieldIfEmpty = function (alternate_field, message) {
+    if (!message) { message = 'One of %s or %s is required.'; }
+    var validator = function (form, field, callback) {
+        var alternateBlank = trim(form.fields[alternate_field].data).length === 0,
+            fieldBlank = trim(field.data).length === 0;
+        if (alternateBlank && fieldBlank) {
+            callback(util.format(message, field.name, alternate_field));
+        } else {
+            callback();
+        }
+    };
+    validator.forceValidation = true;
+    return validator;
+};
+
 exports.min = function (val, message) {
     if (!message) { message = 'Please enter a value greater than or equal to %s.'; }
     return function (form, field, callback) {
diff --git a/test/test-validators.js b/test/test-validators.js
index 35bfd04..032419d 100644
--- a/test/test-validators.js
+++ b/test/test-validators.js
@@ -21,6 +21,39 @@ exports.matchField = function (test) {
     });
 };
 
+exports.requiresFieldIfEmpty = function (test) {
+    var v = validators.requiresFieldIfEmpty('alternate_field', 'field 1: %s field2: %s'),
+        empty_fields = {
+            field: {name: 'field', data: ' '},
+            alternate_field: {name: 'alternate_field', data: ''}
+        },
+        filled_fields = {
+            field: {name: 'field', data: 'filled'},
+            alternate_field: {name: 'alternate_field', data: 'also filled'}
+        },
+        first_filled = {
+            field: {name: 'field', data: 'filled'},
+            alternate_field: {name: 'alternate_field', data: ''}
+        },
+        second_filled = {
+            field: {name: 'field', data: ''},
+            alternate_field: {name: 'alternate_field', data: 'filled'}
+        };
+    v({ fields: empty_fields }, empty_fields.field, function (err) {
+        test.equals(err, 'field 1: field field2: alternate_field');
+        v({ fields: filled_fields }, filled_fields.field, function (err) {
+            test.equals(err, undefined);
+            v({ fields: first_filled }, first_filled.field, function (err) {
+                test.equals(err, undefined);
+                v({ fields: second_filled }, second_filled.field, function (err) {
+                    test.equals(err, undefined);
+                    test.done();
+                });
+            });
+        });
+    });
+};
+
 exports.min = function (test) {
     validators.min(100, 'Value must be greater than or equal to %s.')('form', {data: 50}, function (err) {
         test.equals(err, 'Value must be greater than or equal to 100.');