Aims. To analyze the association between alcohol intake and the severity of injuries sustained from traffic accidents on a Mexican highway. Design. An observational unit evaluated drivers involved in auto accidents. Setting. Mexico-Cuernavaca Highway, Mexico. A 60 km-long road with many altitude variations and sharp curves. Participants. Three hundred and eighty-six drivers involved in traffic accidents between March and September, 1994. Measurements. A questionnaire was applied to the driver, an occupant or witness at the site of the accident to collect information about the driver, vehicle characteristics, type of accident, day-night occurrence, road section (Mexico-Cuernavaca or CuernavacaMexico) and weather conditions. A physical examination was carried out to determine the presence and severity of injuries. Findings. There were 177 injured people, including 12 deaths, with rates of 67.5 injuries and 4.58 deaths per 10 000 km driven. Variables associated with alcohol intake ( p 0.05) included: severity of injuries, non-use of seat belt, vehicle size and occurrence at night. Risk factors for severe injuries were: alcohol intake (adjusted OR 6.1 CI 95% 1.6-24.0); non-use of seat belt (OR 4.9 CI 2.2-10.8), age 25 years (OR 3.6 CI 1.0-12.7), age 54 years (OR 6.0 CI 1.4-25.0), speed 90 km/h (OR 2.6 CI 1.1-6.3) and occurrence at night (OR 2.6 CI 1.3-5.3). Conclusions. Alcohol intake is a major risk factor for severe injuries from highway traffic accidents. Its association with other risk factors such as non-use of seat belt and excessive speed suggests the importance of designing interventions aimed at reducing alcohol intake among automobile drivers.