To characterize the clinical features of patients with acute cerebral infarction who sustained intracerebral hemorrhage related to heparin anticoagulation, we describe 10 patients and review reports of 16 cases. Cardiac-source embolism was identified in seven (70%) of the 10 patients and consisted of atrial fibrillation in six of the seven. The middle cerebral artery territory was affected in nine patients (90%), with moderate-sized or large infarcts by clinical and computed tomographic criteria. The interval between stroke onset and intracerebral hemorrhage was less than 72 hours in 80% of the patients. Intracerebral hemorrhage occurred less than or equal to 24 hours after the time heparin was started in 80% of the patients. The activated partial thromboplastin time closest to the time of intracerebral hemorrhage was greater than 2 x control in seven patients. Our findings in the 10 patients are similar to those of the 16 cases previously reported and suggest that heparin-related intracerebral hemorrhage occurs early after stroke onset, usually with moderate-sized or large infarcts, and with excessive anticoagulation in some patients.