Our aim was to compare risk of lung cancer associated with smoking by gender and histologic type. A total of 30,874 subjects, 44% women, from three prospective population-based studies with initial examinations between 1964 and 1992 were followed until 1994 through the National Cancer Registry. There were 867 cases of lung cancer, 203 among women and 664 among men. Rates among female and male never-smokers were similar, although confidence intervals around rates were wide. Rate ratios (RRs) increased with number of pack-years for both men and women to a maximum of approximately 20 in inhaling smokers with more than 60 pack-years of tobacco exposure. RRs did not differ much between men and women: adjusted for pack-years, age, and study population, the ratio between female and male smokers' RRs of developing lung cancer was 0.8 (95% confidence interval = 0.3-2.1). All histologic types were associated with smoking, with the largest RR seen for squamous cell carcinoma and anaplastic carcinoma. This prospective population-based study does not confirm previous reports from case-control studies of a higher relative risk in women than in men for lung cancer associated with smoking.