When is the outlook hopeless after rupture of an intracranial aneurysm? Some data bearing on the answer to this important question were obtained in a prospective, multicenter trial of 184 poor grade patients in a study of the calcium antagonist nimodipine. Entry was within 3 days of subarachnoid hemorrhage (SAH). The admission work-up included angiography of the anterior and posterior circulations and computed tomographic (CT) scans. The angiograms were repeated as close to Day 8 post-SAH as possible, and the CT scans were repeated at 3 months at the time of follow-up neurological assessment. Radiological assessment was performed independently of knowledge of drug treatment or patient outcome. A discriminant function analysis indicated that the relative importance of factors prognostic for outcome was, in order of importance: whether the patient was treated surgically, neurological grade on admission, age, initial systolic blood pressure, and aneurysm size. The discriminant function analysis correctly classified 80% of our cases. A constellation of poor prognostic features will aid the neurosurgeon in treating a patient conservatively and appropriately advising relatives. The ultimate decision on how to treat a given patient continues to depend partly on clinical judgement, which remains intuitive and subject to influences not studied here.