Lung cancer is the most common cancer in the world. In men, the highest incidence rates are seen in Europe (especially eastern Europe) and North America. In women, high incidence rates are found in North America and in Europe, particularly in northern and western Europe. It is estimated that there were about 375000 cases of lung cancer in Europe in 2000; 303000 in men and 72000 in women. The number of resulting deaths was about 347000 (280000 in men and 67000 in women). Tobacco smoking is well established as the main cause of lung cancer and about 90% of cases are thought to be tobacco related. There is a clear dose-response relation between lung-cancer risk and the number of cigarettes smoked per day, degree of inhalation, and age at initiation of smoking. Someone who has smoked all their life has a lung-cancer risk 20-30 times greater than a non-smoker. However, risk of lung cancer decreases with time since smoking cessation. Recently, there has been renewed interest in screening because spiral computerised tomography can detect small asymptomatic lesions more effectively than conventional radiography. Although cure rates for such lesions are very good, there is to date no evidence for effectiveness of mass-screening strategies.