The diagnostic dilemma to differentiate angiomyolipomas from renal cell carcinoma has been resolved by computerized tomography and sonography. However, these imaging modalities are incapable of estimating the functional contribution of individual kidneys. Renal scintigraphy can be used for a quantitative impression of renal function and is, therefore, of additional value in monitoring conservatively treated tuberous sclerosis patients as shown by the case report.