Abstract The aim of this study was to evaluate self-reported syphilis and associated factors in sexually active young adults (16-25 years old) in the Public Health System in Brazil. This was a cross-sectional study with 8071 participants recruited from 119 primary care units. Of these, 224 (2.86%, 95% CI 2.29-3.43%) reported having the disease. Age, lower socio-economic class, being a smoker, not using a condom at first sexual intercourse, and ever had a same-sex sexual experience were associated with syphilis. The results reinforce the importance of implementing strategies focused on socio-economic class and early sexual education that encourage condom use from the beginning of sexual activity.