In a prospective study involving a total of 87 ventriculostomies, ventriculostomy-related infections (based upon a bacteriological definition) developed in 15 patients (17.2 per cent). Intraventricular haemorrhage was related to a higher infection rate. Infection was most frequent within the first days after the external ventricular drain (EVD) was inserted. There was no relation between infection and the number of manipulations of the EVD or antibiotic treatment during the time of EVD placement.