Thirty-six patients with acute spontaneous subarachnoid hemorrhage (26 caused by rupture of an aneurysm) were examined by transcranial color-coded real-time sonography by using a 2.25-MHz ultrasound transducer. In 20 of these 26 patients (76%), the aneurysm could be identified by a characteristic abnormal blood flow pattern within the aneurysm in coronal and axial scanning planes by transcranial color-coded real-time sonography. Blood within the basal cisterns, on top of the tentorium, and within the ventricles and parenchyma was sonographically detected by increased echodensity in 75%. In addition, cerebrospinal fluid circulation disturbances and cerebral vasospasm were detected in two-dimensional B-mode images in 85% and 100%, respectively. In Doppler mode, intravascular blood flow velocity could be quantified. We conclude that transcranial color-coded real-time sonography, a new, noninvasive method for diagnosis and follow-up of patients with subarachnoid hemorrhage, allows detection of the primary vascular lesion and monitoring of complications.