Purpose The objectives of this prospective study are to compare intravenous contrast-enhanced (CE) fluorine-18-fluorodeoxyglucose (F-18-FDG) PET/computed tomography (CE F-18-FDG PET/CT) with conventional methods (CT/MRI) and to evaluate the relationship of maximum standardized uptake value (SUVmax) with Fuhrman grade in patients with renal tumors. Patients and methods A total of 62 patients [35 males and 27 females; mean age 55.8 +/- 12.7 (range: 27-81) years] were enrolled in the study. CE F-18-FDG PET/CT scanning included whole-body (early) and abdominal imaging (late) 1 and 2 h after intravenous F-18-FDG administration, respectively. SUVmax was calculated for primary tumors. CE F-18-FDG PET/CT and CT/MRI findings were compared with respect to primary tumors and staging. Results The sensitivity of CE F-18-FDG PET/CT in primary tumor detection was 98%, which was very close to that of CT/MRI (100%). CE F-18-FDG PET/CT resulted in correct staging in 84% of the cases, compared with 68% of the cases with conventional methods (52 vs. 42 patients). SUVmax values of early PET for the primary tumors were significantly correlated with the Fuhrman grades (P<0.001). CE F-18-FDG PET/CT enabled the detection of synchronous tumors in four patients, one of which was incorrectly diagnosed as having metastasis by CT. Distant metastases were detected in 16 patients with CE F-18-FDG PET/CT and in 13 patients with routine conventional methods. Conclusion CE F-18-FDG PET/CT showed similar results compared with CT/MRI in the detection of primary tumors, but it was superior to conventional methods in the detection of metastasis and staging. Given the highly significant correlation between SUVmax values and the Fuhrman grading, CE F-18-FDG PET/CT may play a significant role in the evaluation of patient prognosis.