Summary. Health-risk behaviour in children, its kind and frequency, result from genetic and environmental factors. This survey examined health-risk behaviours (smoking, alcohol drinking and drug abuse, sexual experience) in high school students, the relation of their health-risk behaviours with certain health-risk behaviours in their parents (smoking, alcohol abuse), and interrelations among the examined types of risky behaviours. The study included 1009 of 1144 inquired students (426 girls, 583 boys) of high school (of 5 grammar schools and 4 trade schools) aged 15–19 years (17.50±0.70 years). In the period of time preceding the inquiry (3 months) 55.80% of the students smoked, 74.13% of them drank alcohol, 18.43% took drugs, whereas 45.09% of them previously had sexual intercourse. Children of smokers (n=563) smoke more often (chi-square=17.06, p<0.01), drink alcohol more often (chi-square=16.58, p<0.01), and have sexual experience more often (chi-square=9,84, p<0.01) in comparison with children of non-smokers (n=446). Children of parents who drink alcohol (n=240) drink it themselves more often (chi-square=20.14, p<0.01), take drugs more often (chi-square=27.02, p<0.01), smoke more often (chi-square=5.99, p<0.01), and have sexual experience more often (chi-square=8.33, p<0.01) in comparison with children of non-drinking parents (n=769). Certain kinds of health-risk behaviours show a tendency to form clusters, i. e. among the examinees, there are 287 students (28.44%) smoking, drinking alcohol and with sex experience at the same time. Almost every tenth examinee has all four health-risk behaviours (100 students, 9.91%). Only every seventh student has none of the health-risk behaviours (136 students, 13.48%), making 6 of 7 examinees positive in at least one of the risky behavioural types (873 students, 86.52%). In conclusion, the paper confirms a strong influence of parental health-risk behaviours on their children’s health-risk behaviours. Therefore, preventive measures should be at least bidirectional, addressed not only to students, but to their parents as well.