Increasing rates of incidence and mortality from lung cancer were noted in the 1930s and smoking was one of a number of suggested causes. Various workers in 1950 published persuasive confirmation from case–control studies, which showed a large relative risk for cigarette smokers, increasing with amount smoked. Prospective cohort studies provided further confirmation and showed that other causes of death are involved. The effect of passive smoking is discussed. Although smoking has been reduced in developing countries, concern exists about the lesser degree of reduction by women or by poorer people, and about the targeting of developing countries in tobacco promotion.