Of 838 patients with severe head injuries admitted since the introduction of computerized tomography, 211 (25.1%) talked at some time between trauma and subsequent deterioration into coma. Of these 211 patients, 89 (42.2%) had brain contusion/hematoma, 46 (21.8%) an epidural hematoma, 35 (16.6%) a subdural hematoma, and 41 (19.4%) did not show focal mass lesions. Thus, four of every five patients who deteriorated into coma after suffering an apparently nonsevere head injury had a mass lesion potentially requiring surgery: the mass was intracerebral in 52.3% of the cases and extracerebral in 47.6%. Patients aged 20 years or less had a 39% chance of having a nonfocal mass lesion (diffuse brain damage), a 29% chance of having an epidural hematoma, and a 32% chance of having an intradural mass lesion; patients over 40 years had only a 3% chance of having a nonfocal mass lesion, an 18% chance of having an epidural hematoma, and a 79% chance of having a intradural mass lesion. Sixty-eight (32.2%) patients died and 143 (67.8%) survived. The following were independent outcome predictors (in order of significance): Glasgow Coma Scale score following deterioration into coma, the highest intracranial pressure during the patient's course, the degree of midline shift, the type of intracranial lesion, and the age of the patient. In contrast, the mechanism of injury, the verbal Glasgow Coma Scale score during the lucid interval, and the length of time until deterioration or until operative intervention did not influence the final result.