Page Submits Twice

Here is the sample code for my form, but problem is that it submitts
twice in some cases when i click sub mit button.

<script>
function validateform (){
//do a lot validation here, if validation failes, return false;

//finaly this line
return true;
}
</script>

<form name="abc" action="any other apge" onsubmit = "return
validateform();">

<input type="submit" name="save" id="save">
</form>