Objective  To investigate the status and influencing factors of sexual behaviors among medical undergraduates.

  Methods  An anonymous questionnaire survey on demography, sexual behavior and relevant attitudes and factors was conducted among 9 950 undergraduates in a medical university in Xi’an city between December 2015 and June 2016. Then the participants reporting sexual behaviors were selected as the cases and those not reporting sexual behaviors as the controls.Univariate analysis with chi-square test and multivariate analysis with logistic regression were performed.

  Results  The self-reported rate of sexual behavior was 4.32 % (430/9 950) among the undergraduates. Of the participants with sexual behaviors, the males reported a high ratio of commercial sex compared to the females (13.6 % 37/273 vs. 4.3 % 6/139, P < 0.01) and 12.5 % (33/265) of the males reported homosexual behavior. The results of logistic regression analysis demonstrated that grade (odds ratio OR = 0.65, 95 % confidence interval 95 % CI: 0.55 – 0.78), monthly living expenses (OR = 0.65, 95 % CI: 0.52 – 0.80), marriage status (OR = 0.55, 95 % CI: 0.44 – 0.71), receiving sexual education (OR = 1.77, 95 % CI: 1.15 – 2.71), attitude towards premarital sexual behavior (OR = 1.30, 95 % CI: 1.04 – 1.64), attitude towards the lover’s history of sexual behavior with other partners (OR = 0.69, 95 % CI: 0.52 – 0.91), attitude towards homosexuality (OR = 1.51, 95 % CI: 1.14 – 21.99), and estimation on the prevalence of sexual behavior among classmates (OR = 1.62, 95 % CI: 0.56 – 0.68) were significantly associated with sexual behavior among the graduates.

  Conclusion  The prevalence rate of sexual behavior is relatively low and relates closely to attitudes towards sexual behavior among medical undergraduates.