As part of a world survey of the habits, knowledge and attitudes of medical students regarding tobacco we report a study in 15 medical schools from nine Asian countries. Some 1646 first year and 1587 final year students were included, of whom 59% were male. The prevalence of daily smoking in males was 4% in first year and 11% in final year; of occasional smoking 18% and 24% respectively, both with considerable variations between countries. The rates were very low in women. Male exsmokers varied from 3% to 24% in different centres. Overall, 33% of smokers had made a serious attempt to quit; 44% expected to have succeeded within 5 years. Over 80% of non- or exsmokers, but only 60% of smokers, thought smoking was harmful to health. There was gross underestimation of tobacco's causal role in a number of important diseases, e.g. coronary artery disease, peripheral vascular disease, emphysema, bladder cancer and neonatal mortality. There were notable defects both in training and in motivation to counsel smoking patients. There was only partial knowledge of legislative and other measures to discourage smoking, e.g. only 44% of final year students (26% of smokers) thought increased taxation an important measure. In knowledge and attitudes there was little difference between the sexes, but in most aspects smokers had notably lower scores.