A retrospective study was performed at two teaching hospitals--one in the United States and one in Canada--to determine the results of computed tomography (CT) examinations of the head in patients with nontraumatic headache. Of 1111 examinations performed over a 3-year period, 120 (10.8%) demonstrated an acute intracranial abnormality, such as hemorrhage, infarction or tumour; the frequency of such abnormalities was highest among inpatients and subjects over 40 years of age. Cranial and extracranial abnormalities, such as sinusitis and metastases to the calvarium, were found in 40 (3.6%) of the cases. Chronic abnormalities, such as cerebral atrophy or remote infarction, were the most significant findings in 202 (18.2%) of the cases. The cost of finding each case of acute intracranial abnormality was $5962 (US); for subarachnoid hemorrhage among patients in the emergency department, it was $15,837 (US).