Acute renal failure has been observed in patients undergoing angiography in which a hypertonic triiodinated contrast medium is used. To ascertain the incidence of renal dysfunction and the clinical risk factors, we did a prospective study in which creatinine clearance was measured before and immediately after 120 arteriographic procedures. Thirty-seven patients (31%) sustained a significant reduction in creatine clearance after arteriography. No specific risk factor could be determined. Our findings, however, indicate that patients with preexisting renal insufficiency or diabetes mellitus are not at a higher risk for sustaining a fall in creatinine clearance after angiography.