In a retrospective study of 300 children who underwent placement or revision of cerebrospinal fluid (CSF)-peritoneal shunts during a 10-year period, 15 (5%) developed shunt-related abdominal complications with ventricular sepsis and two developed acute perforated appendicitis. Abdominal complications and associated shunt infections suggested two potential modes of development: (1) descent of contaminated CSF from an infected shunt into the abdomen (CSF ascites--four patients, CSF pseudocysts--four patients, and shunt-induced abscess/peritonitis--five patients); and (2) ascent of bacteria into the shunt from an abdominal source (visceral perforation by the shunt catheter--two patients and acute perforated appendicitis--two patients). Three types of shunt systems were placed during the study period; five of the seven (71%) most serious septic complications were associated with the use of Raimondi spring-reinforced catheters. Bacteria isolated in this series were associated with differing modes of sepsis: those involving descent of bacteria into the abdomen from an infected shunt were predominantly gram-positive, cutaneous microorganisms, whereas those associated with ascent of bacteria from the abdomen into the shunt were mixed, gram-negative intestinal microorganisms. Appendicitis did not result in shunt infections. Aggressive treatment resulted in no operative or complication-related deaths. Removal of the shunt catheter from the abdomen and intravenous antibiotics were essential for eradication of sepsis; laparatomy was required only for cases with suspected peritonitis. In eight of the 17 (47%) patients, reestablishment of CSF-peritoneal shunts was performed after resolution of shunt-related complications. In recent years improved shunting materials and supportive care have reduced the incidence of the most serious of these complications.