Studies of the factors that influence smoking behavior, particularly among adolescents are attracting increasing interest among psychologists, health economists, and public health professions. However, since the relationship between attitudes toward smoking and smoking behavior is not well-established, further study is necessary. The purpose of this study was to contribute to the empirical knowledge of determinants of smoking initiation in adolescents. The study used a 3-year longitudinal sample (2000-2002) of young adolescents of a region of Spain, aged 13-14 years at the beginning of the study. Results indicate the influence of social factors, as well as the influence of these attitudes on teenage smoking behavior. It is concluded that external pressures, including smoking at home, are some of the determinants of attitude towards smoking, but that sensitivity to advertising and lifestyles has more influence. Tables, glossary, and references