Both angiotensin converting enzyme inhibitors and nonsteroidal anti-inflammatory drugs can lead to functional renal insufficiency. In an observational study we assessed the frequency of this adverse effect in patients aged over 75 years receiving these drugs in combination. In one year, out of 1500 patients whose records were screened, 12 were prescribed this combination. 2 developed acute renal failure, of whom one died and the other recovered after discontinuation of both drugs. 4 patients showed deterioration in renal function, which returned to normal after one of the drugs was stopped. Renal function remained stable in 6 patients: patients with deterioration in renal function were older and more likely to be on diuretics. This drug combination is commonly nephrotoxic in the elderly and should be avoided, especially in those taking diuretics.