If you want your UIImage to repeat, you must wrap it as a “pattern” and assign it as the background color of a view. Additionally, ensure that you set the opaque on both the layer and the view if you have a semi-transparent image.

More info here:
http://stackoverflow.com/questions/4059487/iphone-uiviews-backgroundcolor-using-a-png-with-transparency 

Edit:
You must set the opaque properties after you set the background image. This is probably due to the rendering engine.