Studies of the prevalence of alcohol and drug abuse among trauma patients have produced recommendations that all trauma patients be screened for these substances. But a national survey of trauma centers showed that just 72.0% of level 1 trauma centers routinely obtain blood alcohol levels on trauma patients and only 50.4% routinely utilize toxicology screens. Utilizing patient summary data collected on 2,246 trauma patients treated in the Emergency Department of Long Beach (CA) Memorial Medical Center over a 2.5 year period, and laboratory results for a random sample of 246 of these patients, this study sought to determine patient and presenting problem characteristics associated with screening and positive test results in centers (such as ours) where screening is done selectively. Results show that 75.4% of trauma patients are screened for blood alcohol levels, and 58.5% are given a urine toxicology, with lowest rates for 12-20 year olds and highest rates for patients over 40 who were confused or incomprehensible. Men were slightly more likely to be screened for blood alcohol than women, but their positivity rate was 2.5 times higher; by contrast, the toxicology positivity rate did not differ significantly by gender. A positive finding for either test was associated with a 40% higher rate of positivity for the other.