Records of coma and post-traumatic amnesia (PTA) were collected for a group of 38 patients with closed head injury. The results confirmed earlier studies indicating that patients may have short or negligible coma but report prolonged PTA. Comparison of eight patients with prolonged PTA (> 7 days) and short coma (< 6 hours) with the rest of the group on MRI in the acute stage showed that these patients had significantly more extensive hemispheric damage. In the group as a whole both coma and PTA were related to the number of areas in central brain structures in which lesions were detected, but only PTA was significantly related to the number of hemispheric areas in which lesions were found. It is concluded that although both coma and PTA are related to brain damage they reflect disparate patterns of lesions. Assessment of PTA can thus provide additional information concerning severity of injury.