In a consecutive series of 160 patients in Hunt and Hess Neurological Grades I to III who were operated upon for a ruptured supratentorial aneurysm within 3 days after the hemorrhage, 42 patients (26%) had an unfavorable outcome. Delayed ischemic cerebral dysfunction with permanent deficit accounted for the unfavorable outcome in 18 patients (43% of all unfavorable results or 11% of the total series), whereas the unfavorable outcome was due to deficit ascribed to surgical trauma in 11 patients (26% of all unfavorable results or 7% of the total series) and to the initial hemorrhage in 7 patients (17% of all unfavorable results or 4% of the total series). Impaired outflow of cerebrospinal fluid with shunt dependency occurred in 3% of the total series. Of the patients with an unfavorable outcome, 17 (40%) had had arterial hypertension before the hemorrhage. The incidence of unfavorable outcome in good grade patients (Grades I and II) was not influenced by timing of operation (Day 1, 2, or 3 after hemorrhage). The results favor the opinion that it is principally the patient's condition during the acute stage that determines the outcome. (Neurosurgery 13:629-633, 1983).