In many patients with subarachnoid hemorrhage (SAH) there is a delay between the onset of symptoms and admission to hospital. An important cause for the delay is an initially erroneous diagnosis. The goal of this study was to determine the frequency of acute confusional state (ACS) as a presenting symptom of SAH and to describe the clinical and radiological characteristics of these patients. We studied all 717 patients registered from January 1989 to July 1997 in the SAH database of the University Medical Center Utrecht. For patients who presented with ACS we reviewed the computed tomography scans for baseline characteristics: the amount of cisternal blood, intraventricular or intracerebral hemorrhage, and hydrocephalus. Details about features of onset were known for 646 patients. Nine patients (1.4%) presented with ACS. In five patients ACS was either preceded by a period of loss of consciousness or accompanied by severe headache. Subtle focal deficits were found at initial neurological examination in four patients. Computed tomography demonstrated a frontal hematoma in three patients and hydrocephalus in four. The site of the ruptured aneurysm was at the anterior communicating artery in four patients, at the internal carotid artery in two, and at the basilar artery in two. In our series, one per 70 patients with SAH presents with ACS. Keys to early diagnosis of SAH in patients presenting with ACS are a preceding period of loss of consciousness and severe headache on neurological assessment.