AIMS: To study the prevalence of adolescents' problematic alcohol use and its parental predictors: drinking habits and socio-demographic factors. DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS: Questionnaires were sent regularly to the same Finnish families (n = 1132) from the onset of pregnancy (in 1986-87) to the child's age of 15 years (in 2001-02) (n = 1028). There was a total of three follow-up points. FINDINGS: At 15 years of age, 83% of girls and 79% of boys had used alcohol; 18% of boys and 14% of girls had been drunk more than once a month. The child's permanent separation from at least one biological parent was the strongest socio-demographic predictor of adolescents drinking. Fathers' present heavy drinking and parental early drinking were the best predictors of their children's problematic alcohol use at the age of 15. CONCLUSIONS: Knowledge of fathers' alcohol use and its time of onset may be used to determine children who are at added risk of problematic alcohol use later in life. Special guidance, support and treatment can be targeted to these families.