To evaluate the incidence, risk factors, and clinical course of radiocontrast nephrotoxic effects in the elderly, 183 patients aged 70 years or more undergoing 199 cardiac catheterizations were studied prospectively. Contrast nephropathy (a rise in creatinine level of greater than or equal to 44 mumol/L above baseline) occurred in 21 cases (11%). In 16 (76%) of these 21 cases, renal function returned toward baseline within several days. One patient developed transient oliguria, but no deaths were attributable to renal failure. Independent risk factors for renal dysfunction included contrast volume greater than 200 mL, serum albumin level less than 35 g/L, diabetes mellitus, serum sodium level less than 135 mmol/L, and baseline creatinine level greater than 133 mumol/L. Renal insufficiency occurred in 1.2% of patients with no risk factors, 11.2% of those with one risk factor, and more than 20% of those with two or more risk factors. Thus, the incidence and clinical course of radiocontrast nephropathy in the elderly are similar to those in younger patients. High-risk elderly patients who may benefit from more aggressive prophylaxis can be prospectively identified, but the threat of contrast nephrotoxic effects should not be considered a major contraindication to angiography in appropriately selected patients.