Prostate cancer, renal cancer, bladder, and other urothelial malignancies make up the common tumors of the male genitourinary tract. For prostate cancer, common clinical scenarios include managing the patient presenting with 1) low-risk primary cancer; 2) high-risk primary cancer; 3) prostate-specific antigen (PSA) recurrence after apparently successful primary therapy; 4) progressive metastatic disease in the noncastrate state; and 5) progressive metastatic disease in the castrate state. These clinical states dictate the appropriate choice of diagnostic imaging modalities. The role of positron emission tomography (PET) is still evolving but is likely to be most important in determining early spread of disease in patients with aggressive tumors and for monitoring response to therapy in more advanced patients. Available PET tracers for assessment of prostate cancer include FDG, 11C or 18F choline and acetate, 11C methionine, 18F fluoride, and fluorodihydrotestosterone. Proper staging of prostate cancer is particularly important in high-risk primary disease before embarking on radical prostatectomy or radiation therapy. PET with 11C choline or acetate, but not with FDG, appears promising for the assessment of nodal metastases. PSA relapse frequently is the first sign of recurrent or metastatic disease after radical prostatectomy or radiation therapy. PET with FDG can identify local recurrence and distant metastases, and the probability for a positive test increases with PSA. However, essentially all studies have shown that the sensitivity for recurrent disease detection is higher with either acetate or choline as compared with FDG. Although more data need to be gathered, it is likely that these two agents will become the PET tracers of choice for staging prostate cancer once metastatic disease is strongly suspected or documented. 18F fluoride may provide a more sensitive bone scan and will probably be most valuable when PSA is greater than 20 ng/mL in patients with high suspicion or documented osseous metastases. Several studies suggest that FDG uptake in metastatic prostate cancer lesions reflects the biologic activity of the disease. Accordingly, FDG can be used to monitor the response to chemotherapy and hormonal therapy. Androgen receptor imaging agents like fluorodihydrotestosterone are being explored to predict the biology of treatment response for progressive tumor in late stage disease in castrated patients. The assessment of renal masses and primary staging of renal cell carcinoma are the domain of helical CT. PET with FDG may be helpful in the evaluation of "equivocal findings" on conventional studies, including bone scan, and also in the differentiation between recurrence and posttreatment changes. The value of other PET tracers in renal cell carcinoma is under investigation. Few studies have addressed the role of PET in bladder cancer. Because of its renal excretion, FDG is not a useful tracer for the detection of primary bladder tumors. The few studies that investigated its role in the detection of lymph node metastases at the time of primary staging were largely disappointing. Bladder cancer imaging with 11C choline, 11C methionine, or 11C- acetate deserves further study.