During 1992-1996, IHS, tribal, or contract-care hospitals recorded 4,491 TBI-related hospitalizations among AI/ANs, resulting in 21,107 hospital days (average length of stay: 4.7 days, range: 1-292 days). The average TBI-related hospitalization rate was 81.7 per 100,000 population (95% confidence interval = 79.1-84.4). Of these 4,491 cases, 221 (5%) were fatal. Male TBI rates were 2.5 times greater than female rates. The AI/AN TBI rate was similar to the combined incidence rate of TBI hospitalizations reported by Colorado, Missouri, Oklahoma, and Utah (81.7 versus 84.8 per 100,000 population),5 but lower than national TBI estimates (98.0).6 The annual AI/AN TBI rate declined by 14% during 1992-1996. The major external causes of AI/AN TBI hospitalizations were motor-vehicle collisions (24%), assaults (17%), and falls (16%). Motor-vehicle–related hospitalization rates were highest among AI/ANs aged 15-24 years (34.2 per 100,000 population). For AI/ANs aged 25-34 years and those aged 35-44 years, assaults were the most common cause of TBI (28.2 and 23.6 per 100,000 population, respectively). Five of the assault cases involved firearms. For AI/ANs aged ≤14 years and those aged ≥45 years, falls were the leading cause of injury (17.7 and 19.4 per 100,000 population, respectively). AI/AN TBI-related hospitalization rates differed by geographic region with the highest rates occurring in the Northern Plains states and Alaska. Of the 1,418 records (32%) of TBI-related hospitalizations coded with "unspecified"* E-codes, 1,309 (92%) were from contract health-care providers.