We reviewed 428 renal arteriograms done during a 5-year period to document the accuracy of angiography in the diagnosis of renal mass lesions and non-function. Subsequently, 198 kidneys (46%) were explored for treatment and diagnostic confirmation. Of the kidneys explored 87 (44%) were radiologically diagnosed as benign cysts. At exploration 6 diagnostic errors were proved, including 3 malignant and 3 benign lesions. The falsely negative malignancy rate was 3% in this category. The angiographic diagnosis of definite tumor was proved to be 100% accurate at operation. However, 3 tumors were benign, representing an 8% falsely positive diagnosis for malignancy. Of the kidneys explored 8% were angiographically diagnosed as being indeterminate. A variety of lesions were found, including 1 benign tumor, 1 malignant tumor and 5 inflammatory lesions. Two malignant lesions were found when exploring angiographically defined hydronephrosis. The remaining kidneys explored carried various diagnoses and were all proved to be correct surgically. Operative mortality was 0.5% but 9 kidneys with benign lesions were sacrificed owing to diagnostic indecision.