Report is presented of three infants in whom subdural hematoma developed as a consequence of surgical treatment for hydrocephalus. This complication was not recognized in the first patient, and was unsuccessfully dealt with in one of the others. Anatomic and physiologic features predisposing to subdural bleeding in hydrocephalic patients are outlined, and methods of prevention, diagnosis, and therapy are described. Success of operation is jeopardized and likelihood is increased of subsequent blindness, convulsions, and mental impairment in a hydrocephalic infant whose precariously adjusted brain is further damaged by this development.