Information about medical students' lifestyles was obtained from 785 second-year students from seven medical schools in Great Britain by a personally administered questionnaire. Fifteen per cent of the students were non-drinkers. Among those who drank, 48% of the men and 38% of the women exceeded sensible weekly limits of alcohol consumption, and high-risk levels of consumption were reported by 12% of men and 7% of women. Cannabis had been used at least once or twice by more than half the men and 40% of the women, and 10% reported regular use (weekly or more often). Experience with other illicit drugs was also reported: amphetamines (8% of students), LSD (7%), ecstasy (4%), amyl/butyl nitrate (10%) and magic mushrooms (7%). Nineteen per cent of the students had used two or more different drugs. Experience with illicit drugs started before entering university in more than a third of those who used them. Comparison of the results with other student surveys suggests that the lifestyles of medical students differ little from those of other student groups, but that alcohol and illicit drug consumption is increasing in university students generally. Prospective studies are under way to establish whether medical students change their lifestyles at later stages of their course and after qualification.