Objective: to evaluate the relationship between the variables individual or group attendance to sexual and reproductive counseling (S&RC) and sexual life onset using: social demographic variables (gender, age, and social security), service attendance concerns, and previous knowledge of sexually transmitted infections and pregnancy in teenagers. Methodology: from September of 2007 to June of 2008 a transversal analytical study was held in 507 teenagers who studied in public schools of Mexico City. The teenagers who accepted to participate in the research were included independently if they had started their sexual life or not. The information was collected using an auto-application questionnaire. In the statistical analysis X2 tests, prevalence ratios and logistic regression models were applied. Results: the male teenagers without health problems had more probability to attend to the group S&RC. Between the ones who had less knowledge about pregnancy prevention methods, this probability was lower. The sexual life onset was more likely between those teenagers from 15 or more years old and without social security. Conclusion: the type of attendance to the S&RC and the sexual life onset can be determined by the teenager's social demographic conditions, their health problems and the pregnancy prevention methods previous knowledge.