This study was undertaken to evaluate the incidence, epidemiology, and temporal relationships of assaults in the State of Illinois from penetrating trauma presenting to Level I and Level II trauma centers, and to project the impact of these variables on hospital staffing. A retrospective analysis was performed on 4 months of data (7/1/92 to 10/31/92) provided by the Illinois Department of Public Health describing consecutive assaults with firearms or knives presenting to all Level I and Level II trauma facilities in the State of Illinois. Data were analyzed for epidemiological parameters including age, gender, and race. Other variables analyzed included trauma score, Glasgow Coma Scale (GCS) score, ethanol levels, urine toxicology results, and mortality. The data were also analyzed for temporal patterns of hospital presentations with respect to the time of day and day of the week. A total of 1,288 cases of penetrating wounds were analyzed. Of these, 881 (68.4%) resulted from firearms and 407 (31.6%) resulted from stab wounds. Ages of all penetrating trauma victims ranged from less than 1 year to 84 years of age. The mean age for firearm victims was 25.0 ± 10.8 (SD) years and 30.5 ± 11.4 years for stabbing victims. Ninety percent of penetrating trauma victims were male and 10% were female. Seventy-two percent of the victims were African-American, 13% Hispanic, 13% Caucasian, and 2% other. Alcohol levels were available for 727 of the 1,288 (56.4%) patients. Of these 727, 433 (59.6%) had measurable levels. The results of drug screens were available for 582 of the 1,288 (45.1%) victims. Of these 582, 208 (35.7%) were positive. Other than alcohol, cocaine was the most frequently detected drug, accounting for 58.4% of the positive drug screens. Firearm victims had significantly lower trauma scores (10.5 v 11.2) and GCS scores (13.2 v 14.3) than stab victims. Significant circadian patterns of penetrating trauma were observed for both types of assaults. For assaults with firearms, the circadian rhythm peaked at 23.1 ± 0.36 hours. For assaults with knives, the circadian rhythm peaked at 23.7 ± 0.44 hours. Weekly patterns were not statistically significant for each individual type of assault. However, when the data were pooled, a weekly pattern peaking on Thursday was observed. These patterns of presentation for assaults are a significant finding that may have implications for hospital staff scheduling of trauma center physicians, nurses, technicians, security, social service, and other ancillary staff.