Despite large investments in prevention, the spread of sexually transmitted diseases (STIs) continues to be a severe problem in Sweden, especially among young people. In Sweden, condoms are recommended for use in tan-dem with another contraceptive in new or casual sexual relationships. Con-dom use to prevent STI transmission differs from its contraceptive in that it must be used in a much larger scale in order to serve as an adequate protec-tion. Here we address questions if—and how—condom use differs between a broad categorization of sexual relationships and sexual practices than what commonly are used in this type of study. Detailed data on the sexual behav-ior of participants during the previous 12 months were collected at nine youth clinics in the Västra Götaland region of Sweden. Participants were sexually active women and men between 15 and 26 years old who visited these clinics for a STI test. Overall, condom use was low irrespective of type of partner and type of sex. Approximately 20 percent of the participants nev-er used condoms during the preceding 12 months. For vaginal sex, the par-ticipants were more likely ‘always’ to use condoms with casual known part-ners as compared to casual unknown partners. If participants had a main or regular partner, they were more likely to use condoms ‘sometimes’ rather than ‘never’ compared to if they had a casual unknown partner. All sexual practices followed this basic pattern. There were few age and sex differ-ences. It is important to understand that young people visiting youth clinics in Sweden—despite efforts to promote condoms use—have unprotected, oral, vaginal, and anal sex, with both known and unknown partners. More effective programs must be developed in Sweden to promote condom use in relationships where the partners are not monogamous as in casual contacts and non monogamous regular contacts (e.g. ‘fuck buddies’).