One hundred consecutive patients with serious illnesses that required angiography were studied prospectively for the development of radiocontrast-induced acute renal failure. The study included 24 diabetics (six diabetics had chronic renal insufficiency), 19 patients with chronic renal insufficiency of other causes, 15 patients with concentrated urine, and 56 patients who received 100 mL or more of a contrast agent. Acute renal failure developed in only one patient. Previous series that indicated much higher incidences were retrospective and not inclusive of all patients, or these studies were composed mainly of patients with diabetic nephropathy and chronic renal failure to whom high doses of a contrast agent were given. Angiography is unlikely to produce acute renal failure except in an occasional patient with well-defined risk factors.