We might anticipate that advances in operating room techniques and postoperative care would reduce the hazards of infection. The experience here reported does not bear this out. In the Massachusetts General Hospital, in 2,148 clean intracranial operations, the overall infection rate was 5.7%, rising to 15% for operations on meningiomas. This modern experience does not compare favorably with the experience of Harvey Cushing, who reported an infection rate of about 1% for operations on meningiomas and an even lower rate for all intracranial operations. The MGH series is broken down into clean intradural procedures, posterior fossa craniotomies, and extradural procedures. The infection rates in each group are further analyzed and each series is accompanied by long, illustrative case protocols. The infection rate goes up in association with the number of times a wound is re-explored and, to a lesser degree, the length of the surgical procedure. Prophylactic antibiotics do not