To assess the need for a trauma system in San Diego County, a concurrent audit of trauma care was performed by an independent consultant in 1982. During the study period from 15 March through 15 June 1982, 591 consecutive major trauma victims (MTV) were collected by the 30 participating hospitals. All medical records, including autopsy reports, were audited for the timeliness and appropriateness of diagnosis and definitive care. Deaths were classified as being not preventable, potentially salvageable, or preventable. A trauma system subsequently became functional on 1 August 1984, with five adult centers and one pediatric center. A Medical Audit Committee composed of physicians and nurses from designated and nondesignated hospitals was organized to perform a monthly concurrent audit of trauma care. Between 1 August and 31 December 1984, 1,366 MTV were triaged to trauma centers. The care of MTV was considered suboptimal in 32% of patients before regionalization, compared to 4.2% after regionalization (p less than 0.01). Preventable deaths occurred in 13.6% of fatalities occurring before implementation of a trauma system, compared to 2.7% after implementation (p less than 0.01). Regionalization of trauma care significantly reduced delays, inadequate care, and preventable deaths due to trauma.