Objective: to analyze the factors that affect use and nonuse of contraception in adolescent and young adults in Costa Rica (between ages 15 - 35). Methods: The influence of personal and socioeconomic characteristics in the decision of the use of contraception can be observed through data collected in the survey National Youth Survey 2007 (Encuesta Nacional de Juventud 2007) and the methodology based on the binary Probit Model with selection bias correction through Heckman. Results: it is showed that the age of both the person and the partner, the stability of the relationship, and residency in urban areas are factors related to lower probability of contraception use. On the other hand, being female, having university education, access to information about birth control and STDs (Sexually Transmitted Diseases), frequency in sexual intercourse, and good supportive family relationships are factors related to higher probability of contraception use. Conclusions: This results could work as a guide to design public policies to prevent teenage pregnancies and STDs. Furthermore, it is important to highlight the significance of sex education for teenagers and their families. This way, education could go beyond encouraging abstinence; it could motivate a responsible sexual life.  
Keywords: contraceptives, adolescent, young adult, Probit model, sample selection, Heckman, Costa Rica