Objectives Early sexual debut is a behaviour that has been associated with acquiring sexually transmitted infections. Higher schooling may delay sexual debut, thus the university population is categorised with low-risk sexual behaviours. The rate ratio of herpes simplex virus type 2 (HSV-2) seroincidence according to demographic characteristics and sexual behaviour was estimated for a cohort of university students.

Methods A dynamic cohort of university students was followed at the Autonomous University of Morelos, in central Mexico, during the years 2001–5. After obtaining informed consent, information was gathered annually regarding demographic characteristics and sexual behaviour and blood samples were obtained to determine HSV-2 antibodies. Seroincidence was estimated and the incidence rate ratio was evaluated using the Poisson regression model.

Results A total of 404 students participated, with 669.2 person-years of follow-up. An incidence of 4.2 cases per 100 person-years was estimated. The variables delayed sexual debut (≥18 years) and multiple sexual partners (two or more sexual partners during the past year) had a rate ratio of 4.1 (95% CI 1.2 to 14.3) and 2.5 (95% CI 1.1 to 5.6), respectively. Incidence for students with delayed sexual debut and multiple partners is estimated to be 10.3 cases per 100 person-years.

Conclusions Delayed sexual debut was a risk factor for acquiring HSV-2, due to a subgroup with sexual debut at 18 years of age or older that had multiple sexual partners; therefore, in the university population that tends to delay sexual debut, it is necessary to implement prevention programmes to promote the decrease of other risky sexual behaviours, as well as the promotion of the consistent use of condoms.