Active smoking remains the main cause of lung cancer. However, one must not neglect the role of occupational exposure, mainly in males and also the role of pollution. In non-smoking females of countries like China, pollution due to the use of charcoal for cooking may represent the main cause for lung cancer. Outside pollution is mainly due to combustion of fossil fuels and to diesel exhaust. Inside pollution is mainly due to environmental tobacco exposure and radon in western countries whereas in developing countries it is mainly due to cooking methods.