Diagnostic pelvic lymphadenectomies are used in both bladder and prostate carcinoma. Enhanced rapid-sequence computed tomographic (CT) scanning of the retroperitoneum and pelvis was done prospectively in patients scheduled for lymphadenectomies. The CT results were then compared to the histopathological findings in 32 patients to analyze the ability of dynamic CT to indicate whether a lymphadenectomy is needed. The comparison showed eight true positive, four false negative, 18 true negative, and two false positive. The sensitivity was 66%, specificity 90% and accuracy 81%. The diagnostic considerations of the role of CT based on these findings are illustrated and discussed.