Positron-emission tomography (PET) employing 18F-labeled deoxyglucose (FDG) has been found to be a highly sensitive and rather specific tool in the detection of a variety of malignant carcinomas. Due to high resolution and outstanding image quality its complementary and supplementary role as compared to morphological methods has increasingly been acknowledged. Urinary-tract malignancies, with the exception of prostate carcinoma, have a rather low incidence and thus experience with FDG-PET is limited. We have compared the diagnostic accuracy of FDG-PET mainly in the primary staging of malignant testicular carcinoma, prostate and renal cell carcinoma. Our data indicate, that FDG-PET is more accurate in the detection of lymph node metastases in malignant testicular cancer as compared to CT, but also fails to detect micrometastases and highly differentiated teratoma. Its role in prostate carcinoma is questionable due to the low metabolic activity of this type of cancer. In all other urinary tract malignancies no final conclusions can be drawn, due to limited experience.