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ImportanceDrunk driving is a major cause of death in North America, yet physicians rarely counsel patients on the risks of drinking and driving.ObjectiveTo test whether the risks of a life-threatening alcohol-related traffic crash were further accentuated by adverse weather.DesignDouble matched case–control analysis of hospitalised patients.SettingCanada’s largest trauma centre between 1 January 1995 and 1 January 2015.ParticipantsPatients hospitalised due to a life-threatening alcohol-related traffic crash.ExposureRelative risk of a crash associated with adverse weather estimated by evaluating the weather at the place and time of the crash (cases) compared with the weather at the same place and time a week earlier and a week later (controls).ResultsA total of 2088 patients were included, of whom the majority were drivers injured at night. Adverse weather prevailed among 312 alcohol-related crashes and was significantly more frequent compared with control circumstances. The relative risk of a life-threatening alcohol-related traffic crash was 19% higher during adverse weather compared with normal weather (95% CI: 5 to 35, p=0.006). The absolute increase in risk amounted to 43 additional crashes, extended to diverse groups of patients, applied during night-time and daytime, contributed to about 793 additional patient-days in hospital and was distinct from the risks for drivers who were negative for alcohol.ConclusionsAdverse weather was associated with an increased risk of a life-threatening alcohol-related traffic crash. An awareness of this risk might inform warnings to patients about traffic safety and counselling alternatives to drinking and driving.