Background: Surveying sexual behavior in the general population serves to identify critical points, monitor the effects, and interpret changes in the spread of sexually transmitted infection. Aim: The aim of this qualitative study was to identify points of particular importance to adolescents’ sexual behavior in order to initiate and design a behavior surveillance programme in Denmark. Methods: We conducted four semi-structured focus group interviews with a total of 19 sexually experienced adolescents aged 18 to 23. Boys and girls were interviewed separately. Each group contained pupils from one Danish Folk High School, but with different social and educational backgrounds. The interview guide was developed from literature reviews and hypotheses based on years of experience with sexually transmitted infections. Data were transcribed verbatim and analyzed using qualitative description. Results: Four major categories of risk behavior were identified: Alcohol consumption is associated with “no condom use”, Nights on the town and meetings in foreign counties or at festivals are associated with one night stands and often lead to unsafe sex, Low self-esteem increases the risk of pushing one’s personal boundaries, thus resulting in promiscuous sexual behavior and Increased sexual experience is associated with lack of condom use. Conclusion: Danish adolescents identified four key elements that could lead to unsafe sex. These results differed slightly from our expectations and will be included in a sexual behavior questionnaire to describe important elements influencing the sexual behavior of Adolescents.