The efficacy of imipenem-cilastatin was compared with that of tobramycin and metronidazole for the treatment of appendicitis-associated abdominal infections in children in an open, randomized trial. Two hundred eighteen patients between 2.5 and 16.8 years of age hospitalized for appendectomy because of suspected acute appendicitis were allocated to 5 treatment groups. The appendix was perforated in 54 (33.8%) of the 160 cases with appendicitis. All patients responded favorably to treatment. Infection in the wound occurred in 15 of 125 (12.0%) of those without preoperative antibiotic therapy and in 5 of 83 (6.0%) of those given imipenem preoperatively (P = 0.12; 95% confidence interval, -2.2 to 14.2%). C-reactive protein decreased significantly faster in those with perforated appendix treated with imipenem than in those treated with tobramycin and metronidazole (58.2 mg/liter vs. 89.4 mg/liter, P less than 0.05 on the third postoperative day). Imipenem-cilastatin was at least as effective and economically comparable as tobramycin and metronidazole for the treatment of appendicitis-associated infections in children.