This paper compares samples of 15-16-year-olds from the UK and France on their usage of alcohol, tobacco and illicit drugs and also seeks to describe the associations between alcohol and other drug use with "family variables" within the two countries. Compared to UK adolescents, French adolescents showed a slightly higher rate of cigarette smoking, were almost identical on cannabis use, rather lower on the use of other illicit drugs and very considerably lower on alcohol use. Family variables were related to substance use. In the two countries, children from non-intact families, those who were not satisfied with their relationships with their father or mother and those who were less closely monitored, were more likely to be heavy substance users than other students. Logistic regressions showed that parental knowledge of the whereabouts of their offspring on Saturday evenings was the strongest factor, in both countries, that family structure is frequently still significant in the UK, and that paternal relationships are highly significant among French students. Differences in national drinking culture, urbanization and parental practices are discussed in an attempt to interpret some of these findings.