Preliminary experience with the occasional good survival of patients in Hunt and Hess Grade IV or V with aneurysmal subarachnoid hemorrhage (SAH) led to a prospective management protocol employed during a 2 1/2 year period. The protocol utilized computerized tomography (CT) scanning to diagnose SAH and to obtain evidence for irreversible brain destruction, consisting of massive cerebral infarction with midline shift or dominant basal ganglia or brain-stem hematoma. These patients, along with those who exhibited poor or absent intracranial filling on CT or angiography, were excluded from active treatment and given supportive care only. All other patients had immediate ventriculostomy placement and, if intracranial pressure (ICP) was controllable (≤ 30 cm H2O without an intracranial clot or ≤ 50 cm H2O in the presence of a clot), went on to have craniotomy for aneurysm clipping. Aggressive postoperative hypertensive, hypervolemic, hemodilutional therapy was subsequently employed. Of 54 patients with poor-grade aneurysms, ventriculostomy was placed in 47 (87.0%) and yielded high ICP's in the overwhelming majority, with the mean ICP being 40.2 cm H2O. Nineteen poor-grade aneurysm patients received no surgical treatment and survived a mean of 31.8 hours with 100% mortality. Thirty-five patients underwent placement of a ventriculostomy, craniotomy for aneurysm clipping and intracranial clot evacuation, and postoperative hypertensive, hypervolemic, hemodilutional therapy. The outcome at 3 months of the 35 patients who were selected for active treatment was good in 19 (54.3%), fair in four (11.4%), poor in four (11.4%), and death in eight (22.9%). It is concluded that poor-grade aneurysm patients usually present with intracranial hypertension, even those without an intracranial clot. Based on radiographic rather than neurological criteria, a portion of these patients can be selected for active and successful treatment. Increased ICP can be present without ventriculomegaly, and immediate ventriculostomy should be performed. As long as ICP is controllable, craniotomy and postoperative intenive care can effect a favorable outcome in a significant percentage of these patients.