Why does my urine smell like butter?

Diet: It is very common to have changes in the odor of urine as a result of what you eat - some foods causes very distinct odors! there are specific medical conditions that can cause changes in the odor of urine (for example, diabetics out of control will have an odor of ketones in their urine). I don't know of any medical condition causing the odor of butter in urine.

Could be serious: Many things can cause changes in the smell of urine but have not heard of any described exactly like butter. A sweet smell may well be an indicator of diabetes or potentially serious metabolic disorder. If it is consistent or persists you should see your doctor.