function dynIFrameSize(){

var parentObject = parent.document.getElementById('dynamischerIFRAME').style;
var THIS = document.getElementById('dynamischerIFRAME');

// höhe anpassen
parentObject.height=(THIS.offsetHeight) + "px";
// breite anpassen
parentObject.width=(THIS.offsetWidth) + "px";

}
window.onload = dynIFrameSize;