Anal intercourse (AI) among heterosexuals is an understudied and taboo subject. This 2017 Swiss national study aimed to describe the characteristics and motivations of heterosexual young adults practicing AI. Participants with any same-sex experience, same-sex attraction or non-heterosexual identity were excluded. The Federal Statistical Office provided the initial sample and potential participants were recruited through postal mail inviting them to an online survey (response rate 15.1%). The sample comprised 3892 participants (52% males; 54% of the overall sample, mean age 26.3 years). Overall, 55% of women and 56% of men had never experienced AI, 17% and 12% had done it once and 28% and 32% more than once, respectively. We found that participants engaging in AI had higher odds of practicing intercourse while intoxicated, being younger at first sexual experience, not using a condom at last intercourse and reporting a history of sexual transmitted infections. The main reason reported by both genders for engaging in their first AI was being curious followed by being in love. In conclusion, AI is a widespread practice among heterosexual young adults and health professionals should be especially attentive to it.