Results of skin cultures obtained before 413 of 505 operations for cerebrospinal fluid-diverting ventricular shunt placement or revision in a pediatric population from April 1980 to May 1983 are analyzed and compared to results of cultures from 20 subsequent shunt infections. Sensitivities to 11 different antibiotics were determined for each isolate cultured. The total operative infection rate was 20 of 505 (4%). Gram-negative bacilli alone accounted for 3 of 20 (15%) shunt infections. One gram-negative bacillus/Staphylococcus aureus infection occurred. Factors predisposing for gram-negative bacillus shunt infection were found in all 4 cases. The majority of shunt infections were caused by typical resident skin organisms: Staphylococcus epidermidis alone, 9/20 (45%); Staphylococcus aureus alone, 4/20 (20%); Corynebacterium sp., 1/20 (5%); alpha-Streptococcus with S. epidermidis, 1/20 (5%); and Micrococcus with S. epidermidis, 1/20 (5%). Only 4 (20%) of the 20 shunt infections were due to organisms identical to those originally grown from the skin. Another 4 (20%) seemed to be infected with a strain of organism different from that initially recovered from the skin. The remaining skin organism shunt infections may or may not have come from the patient's skin. The data suggest that not all skin organism shunt infections arise from contamination by resident skin bacteria at the incision sites at the time of operation. Alternate sources for the infecting organisms are discussed. The antibiotic sensitivity data on skin isolates and shunt isolates suggest that vancomycin is the antibiotic best suited for prophylaxis against shunt infection at our institution.