Although noninvasive imaging modalities can be used to initially detect retroperitoneal masses, angiography is still desirable for several reasons in those cases in which surgery is contemplated. The latter can forewarn the surgeon as to possible hemorrhagic complications in highly vascular lesions. In some cases it can predict the malignant potential of the lesion. Finally, since these masses may derive blood supply from multiple sources, a vascular "road map" is provided to the surgeon. The angiographic findings of malignant retroperitoneal tumors are well known, but very little has been published dealing with benign nonneoplastic retroperitoneal masses. We have performed angiography in 11 surgically proven nonneoplastic retroperitoneal masses (9 inflammatory lesions, 2 hematomas). Major arterial or renal displacement occurred in 10. The 2 hematomas and 3 inflammatory lesions were totally avascular; 6 of the 9 inflammatory lesions revealed fine neovascularity and 5 of these 6 had an associated capillary blush. Sources of vascular supply included the lumbar, renal capsular, superior mesenteric, and gastroduodenal arteries. Although angiography is helpful in preoperative evaluation of retroperitoneal masses for the aforementioned reasons, it may be difficult or impossible to differentiate benign from malignant lesions based on the angiographic findings alone.