This cross-sectional study investigated the prevalence rates of different categories of youth risk behaviour by age, sex and parental education. The study population consisted of 26,111 Hong Kong students, aged 10-19 years, recruited from 48 primary (primary grades 4-6) and secondary schools (secondary grades 1-7). Less than one-third of subjects participated in vigorous exercise regularly, about one-third consumed an unhealthy diet frequently, 18% had tried smoking, and 14.5% had seriously considered attempting suicide. Although only 3.4% of students reported experience of sexual intercourse, less than half used a contraceptive device. Older students had higher prevalence rates of health-compromising behaviours than younger students. Female students were more likely to report suicide-related behaviour, attempting weight loss, and non-participation in vigorous physical activities. Students with parents of a lower educational background were more likely to report rarely or never wearing seat belts and bicycle helmets, suicide-related behaviour, smoking, sexual intercourse before 13 years of age, and attempting weight loss. The availability of data on youth health risk behaviours would enable health educators, public health practitioners and clinicians to plan appropriate screening and counselling for risk behaviours in early adolescents.