PET is a new method for staging malignant tumors; the metabolism is examined and not the morphology. In this study the staging of renal cell carcinoma (RCC) by PET was investigated. In 29 patients PET with fluorodeoxyglucose (FDG) was carried out preoperatively; the PET results were compared to the histology of the OR specimen. In 26 patients a RCC was found histologically, which was diagnosed correctly by PET in 20 patients; in 6 patients a false-negative PET result was obtained. An angiomyolipoma, a pericytoma and a pheochromocytoma showed a false-positive PET result. For lymph-node staging positive nodes were found in 3 patients, which was correct; no false-negative result was obtained. In 25 patients the PET result was true-positive; once a false-positive finding occurred. In conclusion, PET offers the advantage that no allergy to FDG is known and a pacemaker or metal implants are not contraindications; in diagnosing RCC, according to our results there is no further advantage of FDG-PET in comparison to standard methods; for lymph node staging the results are equivalent.