Character Movement

Sorry if this has been covered before because well its a very simple conscept but I can not seem to be able to find the answer to it. I am trying to register two key presses at the same time. For instance if I want my character to move diagonally I would press UP and LEFT or something like that. However my old way of doing this was with the isDown function which they have decided to remove from AS3.0 so I was trying listeners but they only register the last key pressed down. This is my code:

stage.addEventListener(KeyboardEvent.KEY_DOWN, keyHandler);
function keyHandler(event:KeyboardEvent):void {
if (event.keyCode == 37) {
PlayMove.x = PlayMove.x - 1;
if (event.keyCode == 38) {
PlayMove.y = PlayMove.y - 1;
if (event.keyCode == 39) {
PlayMove.x = PlayMove.x + 1;
if (event.keyCode == 40) {
PlayMove.y = PlayMove.y + 1;

Hopefully someone can help me out. Thanks.