Fixed #1599 as Brandon suggested to ignore negative values to width and height css. The fix itself is slightly different as it was moved to .css() instead of staying in .attr() like in his patch. I decided there was less chance of incorrect behavior (like if someone had an XML file with a width attribute that could be negative). Also took out some unneeded white space while I was in there.

src/core.js

@@ -43,7 +43,7 @@ jQuery.fn = jQuery.prototype = {
 			return this;
 
 		// Handle HTML strings
-		} else if ( typeof selector  == "string" ) {
+		} else if ( typeof selector == "string" ) {
 			// Are we dealing with HTML string or an ID?
 			var match = quickExpr.exec( selector );
 
@@ -194,6 +194,9 @@ jQuery.fn = jQuery.prototype = {
 	},
 
 	css: function( key, value ) {
+		// ignore negative width and height values
+		if ( (key == 'width' || key == 'height') && parseFloat(value) < 0 )
+			value = undefined;
 		return this.attr( key, value, "curCSS" );
 	},
 
@@ -360,7 +363,7 @@ jQuery.fn = jQuery.prototype = {
 
 			if ( this.length ) {
 				var elem = this[0];
-		    	
+
 				// We need to handle select boxes special
 				if ( jQuery.nodeName( elem, "select" ) ) {
 					var index = elem.selectedIndex,
@@ -1321,7 +1324,7 @@ jQuery.each([ "Height", "Width" ], function(i, name){
 			this[0] == document ?
 				// Either scroll[Width/Height] or offset[Width/Height], whichever is greater (Mozilla reports scrollWidth the same as offsetWidth)
 				Math.max( document.body[ "scroll" + name ], document.body[ "offset" + name ] ) :
-        
+
 				// Get or set width or height on the element
 				size == undefined ?
 					// Get width or height on the element

test/index.html

@@ -20,6 +20,7 @@
 	<h2 id="userAgent"></h2>
 	
 	<!-- Test HTML -->
+	<div id="nothiddendiv" style="height:1px;background:white;"></div>
 	<dl id="dl" style="display:none;">
 	<div id="main" style="display: none;">
 		<p id="firstp">See <a id="simon1" href="http://simon.incutio.com/archive/2003/03/25/#getElementsBySelector" rel="bookmark">this blog entry</a> for more information.</p>

test/unit/core.js

@@ -410,6 +410,15 @@ test("jQuery.css(elem, 'height') doesn't clear radio buttons (bug #1095)", funct
 	ok( ! $(":checkbox:last", $checkedtest).attr("checked"), "Check last checkbox still NOT checked." );
 });
 
+test("width()", function() {
+	expect(2);
+
+	$("#nothiddendiv").width(30);
+	equals($("#nothiddendiv").width(), 30, "Test set to 30 correctly");
+	$("#nothiddendiv").width(-1); // handle negative numbers by ignoring #1599
+	equals($("#nothiddendiv").width(), 30, "Test negative width ignored");
+});
+
 test("text()", function() {
 	expect(1);
 	var expected = "This link has class=\"blog\": Simon Willison's Weblog";