Sulfamethoxazole 和trimethoprim之複合劑(cotrimoxazole)常被用來治療長期複雜性的泌尿道感染。磺胺劑容易在酸性尿液中沉澱。我們報告一位91歲病患，因為急性尿閉症置放導尿管並且接受數週cotrimoxazole治療。常病患接受經尿道攝護腺切除手術時，同時發現膀胱中有許多扁平黃褐色結石。結石成份經由紅外線光譜分析儀化驗證實是N4-acetyl-sulfamethoxazole結石。此結石屬cotrimoxazole之代謝物。我們認為N4-acetyl-cotrimoxazole結石雖然很少在英文文獻中被報導，但是其發生應該常被忽略。我們建議當必須使用cotrimoxazole磺胺劑，尤其必須長期使用或者原先尿液偏酸性之病人，在服藥同時應該多喝水並且注意N4-acetyl-sulfamethoxazole結石產生的可能性。

The combination of sulfamethoxazole and trimethoprim (cotrimoxa-zole) is frequently used for the purpose of long-standing or complicated urinary and genital tract infection. Sulfona-mides are known to precipitate in the urine, especially in urine with an acidic pH. Herein, we re-port a 91-year-old male who was admitted because of acute urinary retention. He underwent transurethral resection of the prostate (resected adenoma: 52g) smoothly. During the operation, multiple flat, yellow-brownish stones were noted. Stones, analyzed by infrared s pectrophotome- ter, proved to be N4-acetly-sulfamethoxazole stone is rare but possibly under-diagnosed and there are few recent relevant articles in the Englis literature. It is reasonable to take a cautious attitude toward the use of cotrimoxazole as a long-term treatment especially in patients who already have acidic urine. (J Urol R.O.C., 9:29-31,1998)