Triamterene (TA) is a mild ‘potassium-sparing’ diuretic usually employed in combination with other more potent diuretics in the treatment of hypertension. TA pharmacokinetics and pharmacodynamics in normal volunteers, elderly subjects and in patients with renal and hepatic dysfunction are reviewed. A variety of adverse renal effects, such as abnormalities in urinary sediment, nephrolithiasis, interstitial nephritis and acute renal failure, has been reported to occur and is also reviewed. Of particular concern with the increased availability of ‘over-the-counter’ nonsteroidal anti-inflammatory medications (NSAID) is the adverse interaction between TA and NSAID which may culminate in acute renal failure. Although a rare occurrence, the clinician should be aware of potential adverse reactions associated with the use of TA.