Primary purpose of the study: to describe sexual behavior of Prep users, whatever mode of intake, ie continuous or on-demand; it has been shown in some studies, an increase of sexual risks in Prep users, and therefore an similar increase of STIs (sexually transmitted diseases); using a self-questionnaire, we'd like to evaluate sexual behavior before, and 6 months after, starting Prep.

Secondary purposes: to describe medical characteristics of Prep users (past medical condition, demographic characteristics, vaccinations, kidney function, serological results, urine and anal/pharyngeal swabs), clinical and biological Prep safety, STIs occurrence, and antibiotic prescriptions, continuous or on-demand intake, Prep indication.

Inclusion Criteria:

• non HIV-infected subjects
• men aged 18 years or older
• having non protected sexual relationship
• taking Prep (emtricitable/tenofovir disoproxil fumarate) either every day, or on-demand
• affiliated to social security

Exclusion criteria:

• HIV-infected patients
• refusal of study participation
• not on Prep
• not fluent in French language
• safeguarding justice
• on guardianship or trusteeship

Non HIV-infected subjects, who have a high risk to be infected by HIV, mostly because of non protected sexual intercourse.

Most of them are MSM (men who have sex with men). And who started Prep (emtricitable/tenofovir disoproxil fumarate), or will initiate Prep