OBJECTIVE It is well established from pediatric experience and animal experiments that intracerebral blood can be demonstrated by B-mode real-time duplex scanning. This has recently become feasible in adults as well. The present study investigated the changes in the sonographic appearance of intracerebral hematomas over the course of time. METHODS Starting in May 1991, 23 consecutive patients with intracerebral hematoma confirmed by computed tomography (21 spontaneous and 2 traumatic hematomas) were investigated within 1 year. They were monitored by repeated ultrasound scanning via the transtemporal approach. The sonographic appearance of the hematomas on B-mode scans and the angle-corrected blood flow velocity in the basal cerebral arteries were assessed. RESULTS There was unequivocal localization of the hematoma in 18 patients (78%). In 3 cases (13%), an adequate acoustic window could not be found. One small intracerebral hemorrhage was overlooked, and one extensive hemorrhage in the basal ganglia was misdiagnosed as a lobar hematoma. There was an alteration of the appearance of the hematoma with time. This was divided into three sonographic stages (initial stage, days 1 to 5; intermediate stage, days 6 to 10; and capsular stage, from day 10). In 14 of the 20 patients with an appropriate acoustic bony echo window, the blood flow velocity in the middle cerebral artery could be measured; in 1 of these patients, the signs of increasing intracranial pressure were apparent from Doppler frequency spectrum. In 5 patients, the intracerebral hematoma could be imaged but not the ipsilateral middle cerebral artery. One female patient showed cerebral circulatory arrest at the time of examination, which took place within 24 hours after the onset of clinical symptoms. CONCLUSIONS Most intracerebral hematomas in adults can be imaged in B-mode. Their sonographic appearance changes over the course of the disease. The advantages of this noninvasive method are its easy bedside operation and its suitability for follow-up; it is also less stressful than other imaging procedures. It yields a combination of structural and functional diagnostic information. In approximately 13% of the cases, the investigation was not feasible because of inadequate ultrasonic penetration of the intact skull.