To determine levels of alcohol and drugs of abuse in weekend drivers injured in car crashes.This study was the first systematic drug and alcohol testing of blood and urine samples of drivers injured in weekend car crashes in Belgium. Five collaborating hospital in Flanders participated. All injured weekend drivers admitted to the emergency units from July 1, 1994, to June 30, 1995, were included in the study sample. Sampling times were from Friday at 8 PM to Monday at 8 AM.Of the 211 injured drivers, 47.9% had positive test results for screenings for drugs or alcohol; 35.5% only for alcohol, 6.6% only for drugs, and 5.7% had positive results for both alcohol and drugs. Of the 87 weekend drivers with positive alcohol test results, 8% had a blood alcohol concentration (BAC) level below 80 mg/dL, 25.3% had a concentration between 150 and 190 mg/dL, and 39% had a BAC of 200 mg/dL or greater. There seems to be a consistent association between the consequences of the weekend crashes and the use of alcohol, drugs, or both. More than 50% of those who had negative results for drugs and alcohol could leave the hospital within 24 hours after their car crash. For the majority of those with positive findings for alcohol only or for drugs and alcohol (respectively, 72% and 78%), hospitalization in a general hospital unit or ICU was necessary.The results suggest that testing drivers for use of alcohol alone is insufficient.