Trimethoprim-sulfamethoxazole (TMP-SMZ) was continued for eight to 22 months in four girls with recurrent urinary-tract infections, meningomyeloceles, and neurogenic bladders after usual chemotherapeutic agents proved ineffective. A fifth girl who developed bacteriuria following renal transplantation was also successfully treated with TMP-SMZ. Urine remained sterile in all children while on therapy. Hemoglobin, red cell morphology, white blood count, and serum folate levels remained normal. No undesirable side effects of therapy were encountered. After cessation of therapy in one child, Pseudomonas aeruginosa resistant to TMP-SMZ was cultured from her urine. Long term use of TMP-SMZ was effective in maintaining sterile urine in children with repeated urinary-tract infections, meningomyeloceles, and neurogenic bladders.