Because trauma admission and hospitalization patterns have profound effects on the organization and utilization of urban trauma-care systems, the objective of this study was to identify and analyze these patterns. As an example, admissions to an urban Level I trauma center were reviewed. Retrospective review of all 2029 trauma admissions to a Level I trauma center was conducted from 1993 to 1996. The result was that most trauma patients were young (40% < 30 years of age) and male (74%). Mechanisms of injury were motor vehicle accident (36%), fall (27%), gunshot (17%), stab (7%), assault (6%), and swimming or diving accident (3%). Half of the patients were directly admitted from the scene. Injury Severity Score, length of stay, and mortality were 14.1 +/- 0.3, 10.5 +/- 0.3 days, and 5.1%, respectively. Admissions tended to occur more frequently between 4:00 PM and midnight (46%), between Friday and Sunday (52%), and between July and October (41%). The following patterns were identified: admissions per year decreased (-21%) because of reduced penetrating trauma (-43%, P < .01); pediatric patients (< 15 years) had similar incidence of penetrating trauma as adults (ages 15-45). Length of stay for all mechanisms of injury was not statistically different; most mortalities occurred within the first day (33%, P < .01) or after 6 days (36%, P < .01); early mortality was mainly due to penetrating injury (74%, P < .01), whereas late mortality was related to blunt trauma (92%, P < .01). The conclusion was that admission and demographic patterns were identified, which may be useful in the utilization, modification, and future design of trauma systems.