Positron emission tomography by using H2(15)O whose distribution in the brain reflects a genuine cerebral blood flow was made in 5 patients with suspected intracranial hematomas. It was shown that tunicary hematomas might be diagnosed by positron emission tomography. However, examination of cerebral blood flow was not optimal in this abnormality. Computerized tomography remains the basic method for diagnosing intracranial hematomas and positron emission tomography should be used to evaluate cerebral function.