A case-control study involving interviews with 733 male and 672 female incident lung cancer patients and 1495 population-based controls revealed that cigarette smoking is the dominant cause of lung cancer among men in urban Shanghai. All of the principal cell types were affected, with clear trends of rising risk with increasing intensity and duration of smoking. Far fewer women smoked cigarettes, but the overall risk patterns resembled those among males. Among women, however, smoking accounted for only about one-quarter of all lung cancers and less than 10% of lung adenocarcinomas. The findings lay to rest any doubts about the health hazards of smoking Chinese cigarettes, although smoking is not responsible for the high rates of adenocarcinoma reported among Chinese women.