Forty-seven children, ages 1 to 14 years, with appendicular peritonitis were randomly divided into two groups: 27 were treated with the combination tobramycin-clindamycin and 20 with cephalothin followed by cephalexin. The overall rate of complications was 32%. Patients who had had their symptoms for less than 48 hours before being admitted to hospital had significantly fewer complications than those whose symptoms had lasted longer. Patients treated with tobramycin-clindamycin had significantly fewer wound infections. As clindamycin is effective against anaerobes this observation supports the view that anaerobes play an important role in the infectious complications in peritonitis. In this series, 12 species of aerobes and eight species of anaerobes were cultured from peritoneal fluid. In eight patients only one species was isolated; in the remaining 39 patients 29 different combinations of bacteria were encountered. Early diagnosis and administration of antibiotics preoperatively or during surgery, including clindamycin, metronidazol or tinidazol is recommended in the treatment of children with appendicular peritonitis.