There have not been any population-based surveys in Germany to date on the frequency of various types of sexual behavior. The topic is of interdisciplinary interest, particularly with respect to the prevention and treatment of sexually transmitted infections.Within the context of a survey that dealt with multiple topics, information was obtained from 2524 persons about their sexual orientation, sexual practices, sexual contacts outside relationships, and contraception.Most of the participating women (82%) and men (86%) described themselves as heterosexual. Most respondents (88%) said they had engaged in vaginal intercourse at least once, and approximately half said they had engaged in oral intercourse at least once (either actively or passively). 4% of the men and 17% of the women said they had been the receptive partner in anal intercourse at least once. 5% of the respondents said they had had unprotected sexual intercourse outside their primary partnership on a single occasion, and 8% said they had done so more than once; only 2% of these persons said they always used a condom during sexual intercourse with their primary partner. Among persons reporting unprotected intercourse outside their primary partnership, 25% said they had undergone a medical examination afterward because of concern about a possible sexually transmitted infection.Among some groups of persons, routine sexual-medicine examinations may help contain the spread of sexually transmitted infections. One component of such examinations should be sensitive questioning about the types of sexual behavior that are associated with a high risk of infection. Information should be provided about the potential modes of transmission, including unprotected vaginal, oral, and anal intercourse outside the primary partnership.