A study of knowledge, attitude and practice with regard to tobacco usage was conducted in 1278 boys and 353 girls studying in the final year in various schools in Bombay. The proportion of boys given to one or the other form of tobacco usage (including experimenters/triers) was significantly higher in private English median schools (22.5%) compared to private Indian language schools (6.9%) or municipal Indian language schools (13.8%). There was also a significant difference between the two types of Indian schools. Girls from only Indian language schools were entered into the study and the proportion of tobacco users in them was very low (1.1%). Most (86%) boys who used tobacco were smokers. Hence the detailed analysis is restricted to smokers. Several probable factors influencing smoking behavior were studied. It was found that significantly higher proportion of boys smoked if their father or best friend smoked. Generally boys were more sensitive to best friend's or elder brother's disapproval than to parental. They were well informed about harmfulness of smoking but knowledge about specific health hazards was limited. Most of them had a positive attitude towards nonsmoking and smoking control programmes. Tobacco use has been proven to be a major health hazard. Although its use in adults in India is common, prevalence in adolescents in urban schools is not yet high. Before the situation changes we need to mount anti-tobacco educational programmes and work towards a non-tobacco generation to contain the harmful consequences of tobacco usage.