As part of a larger effort to determine total direct and indirect costs of injury in the United States, national estimates of the numbers and expenditures associated with acute hospitalization due to traumatic injury were derived using data from the 1984, 1985, and 1986 National Hospital Discharge Surveys (NHDS). Estimates of the numbers of hospital episodes and total expenditures are reported in this paper for subgroups of patients defined by age, sex, and body region and AIS severity of the injuries sustained. In 1985 2.1 million individuals sustained a traumatic injury which resulted in hospitalization. Hospital expenditures totaled $11.4 billion inclusive of professional fees. Adolescents and young adults aged 15-44 years accounted for nearly one half of all discharges and total hospital costs. The elderly, who represent only 12% of the population, accounted for an additional one quarter of total discharges and hospital costs. Nearly three quarters of the hospitalizations and one half of total expenditures were for minor (ICD/AIS = 1, 2) injuries. Moderate (ICD/AIS = 3) and severe (ICD/AIS = 4, 5), injuries respectively accounted for 23% and 3% of total episodes and 37% and 11% of total expenditures. Only 12% of patients and 25% of trauma care dollars involved injuries sufficiently severe to require treatment at a trauma center.(ABSTRACT TRUNCATED AT 250 WORDS)