The investigation determined the individual, cultural, familial, and obstetric factors associated with pregnancy in adolescent primiparous. Material and Methods: quantitative, cross-sectional descriptive study, in 168 primiparas between 13 and 19 years old who attended prenatal consultation in twelve health centers in Chilpancingo, Guerrero, Mexico, each participant with their legal representatives and with informed consent. Statistical analysis was based on chi-square distribution to investigate the association between variables, SPSS Version 20 was used. Results: information on the factors that prevail in the occurrence of pregnancies in adolescents: beginning of sexual life at an early age, nonuse, or misuse of contraceptive methods and mother and / or sister with family history of pregnancy in adolescents. Conclusions: individual and family, cultural, and obstetrical factors are determinants of adolescent pregnancy.