Objective. To analyze psychosocial factors associated with the decision to smoke in students 13 to 15 years in Mexico City. Materials and methods. Logistic regression models of Youth Tobacco Survey (n=945) and four Focus Groups (GF) in two secondary schools, conducted in 2011-2012, were used. Results. Factors associated with smoking: a) believe that it is safe (OR=2.4,C195% 1.28-4.7), GF: ability to control over consumption and long-term damage; b) to have at least one smoking parent (OR=1.6, CI95% 1.1-2.3), GF: influence. to start/maintain consumption; c) to have friends who smoke (OR=5.0, CI95% 1.9-13.6), GF: influence to experimentation/ repeat, schools without rules on prohibition and have access to cigarettes (OR=2.1, CI95% 0.9-4.1). Protective factors: a) believe that it is harmful (OR=0.3, CI95% 0.14-0.65), GF: rejection of cohabitation with smokers; b) communication with family (OR=0.5, CI95% 0.36-0.91), GF: appeal to self-care; c) consider is young for smoking (OR=0.2, CI95% 0.12-0.43), GF: knowledge about damage and risk perception. Conclusion. It is necessary to strengthen positive psychosocial skills and strengthen compliance with youth protection legislation.