Hypoxia and hypotension are extracranial insults known to have an adverse effect on the outcome of patients with acute head injury. Arterial oxygen tension, blood pressure and the Glasgow Coma Score on admission of 67 patients seen over a 6-month period were correlated with the outcome at 6 months. With a given level of consciousness the presence of an extracranial insult resulted in a worse outcome than would be predicted. The combination of hypoxia and hypotension was uniformly fatal as was the presence of severe respiratory dysfunction.