The authors analyze a group of 451 shunt operations where 317 patients had hydrocephalus and 23 cases were reported positive after cerebrospinal fluid (CSF) cultures. Staphylococcus was the most frequent bacterial organism found (57%). This retrospective study of 23 patients in whom infection developed following placement of an extrathecal shunt, although not a complete biometric evaluation, shows an incidence of infection of 5%. The authors also indicate the limitations in antibiotic treatment when three significant aspects of therapy are not considered fully: 1. sensitivity of the identified organism, 2. CSF levels of the drug that can be attained, and 3. the pharmacokinetic action of the drug in the CSF.