Three patients were diagnosed with drug-induced tubulointerstitial nephritis: a 72-year-old woman who was using a proton pump inhibitor, an 83-year-old woman who had recently been treated with antibiotics and an 83-year-old man who was using omeprazole. Discontinuation of the medications in question and the initiation of glucocorticoids resulted in improved renal function. In two of these patients, the diagnosis was established by renal biopsy. Acute tubulointerstitial nephritis is an important cause of renal insufficiency. It is characterized by inflammatory changes in interstitial tissue. Frequently prescribed medications such as proton pump inhibitors, antibiotics and nonsteroidal anti-inflammatory drugs may cause acute tubulointerstitial nephritis. Other causes are infections and auto-immune diseases. Renal failure may be reversible when use of the offending drug is discontinued. Partial or total renal insufficiency may, however, persist. Early treatment with steroids seems to improve the recovery of renal function in patients with drug-induced tubulointerstitial nephritis, although the evidence is not conclusive.