A variety of lesions of varying complexity were noted during pathological examinations of the brain in 30 cases of acute severe traumatic coma, of whom 27 survived for less than 10 days. "Diffuse brain damage" were present in all cases and contusions were frequently noted (83 p. 100). The lesions appear immediately after, and are directly related to the injury. Ischemic lesions were present in 66 p. 100 of cases and their mechanisms of production are various and interwoven. The frequency of respiratory difficulties associated with brain injuries is stressed. Two thirds of the cases with brain stem lesions (80 p. 100) were secondary to phenomena related to trans-tentorial herniation. Clinical examinations of these patients with acute severe coma demonstrates the difficulties encountered in assessing prognosis based on clinical findings within the first 48 hours.