Objective To investigate the value of delayed 18F-FDG PET/CT with oral intake small dosage diuretics for diagnosing urogenital cancers.Methods Patients with suspected urogenital system cancers were divided into routine dosage diuretic group (n=12) and small dosage diuretics group (n=35).All patients underwent whole-body PET/CT followed by delayed scanning after oral 40 mg or 20 mg Furosemide respectively.The urine maximum standard uptake value (SUVmax) and T/U (the ratio of urine and lesion SUVmax) before and after diuresis were compared respectively.Diagnostic efficacy for malignant urogenital system cancers of small dosage group was calculated.Results The urine SUVmax and T/U were statistically different between routine whole body and delayed scans in both groups (P＜0.05).SUVmax and T/U of routine and delayed scans had no statistical differences between the two groups (P＞0.05).In small dosage group,the sensitivity,specificity,positive predictive value,negative predictive value and accuracy of delayed imaging and routine imaging was 96.77％ (30/31)and 61.29％ (19/31),75.00％ (3/4) and 50.00％ (2/4),96.77％ (30/31) and 90.48％ (19/21),75.00％ (3/4)and 14.29％ (2/14),94.29％ (33/35) and 60.00％ (21/35),respectively.The sensitivity and accuracy were statistically different between routine and delayed imaging (P＜0.001).Conclusion Delayed PET/CT imaging with oral small dosage Furosemide has the same efficacy as PET/CT using routine dosage diuretics,which is useful for diagnosing urogenital cancers.