Background: In order the aim to evaluate the risk-taking behaviour, a representative study on sexual behaviour of secondary-school students in Slovenia was performed.Methods: In the spring of 2004, 2380 1st and 3rd grade students from 48 randomly selected secondary schools in Slovenia anonymously completed a self-administered questionnaire. Descriptive statistics was used for data analysis.Results: The average students’ age was 15.4 years (1st grade) and 17.4 years (3rd grade). Sexual intercourse had ever had 24 % of boys and 21 % of girls from the 1st grade, and 52 % of boys and 54 % of girls from the 3rd grade. At first sexual intercourse condom was used by 74 % of sexually active 1st grade and by 75 % of 3rd grade students; 6 % of 1st grade and 7 % of 3rd grade students used contraceptive pill. At last sexual intercourse condom was used by 65 % of sexually active 1st grade and by 50 % of 3rd grade students; 11 % of 1st grade and 32 % of 3rd grade students used the pill. Contraceptive methods and sexually transmitted infections are not sufficiently known to the students. Most students (34 %) prefer professionals to be the source of information on sexuality. Two percent of boys and 10 % of girls had ever had at least one sexual contact with the same sex.Conclusions: The percentage of sexually active secondary-school students in Slovenia is high. The use of contraceptive pill is favourable, but the condom use needs to be further promoted.