The importance of cigarette smoking as a risk factor for specific histologic types of lung cancer in men and women has been examined in a case-control analysis of data from the Cancer Surveillance Program of Orange County, a population-based registry. Smoking habits were abstracted from medical records for 1153 men and 833 women diagnosed with primary lung cancer in 1984–1986 and 1851 men and 1656 women aged 30 or older diagnosed with cancers not associated with smoking. Ninety-six percent of men and 89% of women with lung cancer were current or former cigarette smokers, as compared with 55% of men and 34% of women with other cancers. The age and ethnicity-adjusted odds ratios (OR) for ever-smoking were 19.7 for men and 15.0 for women. Men and women who smoked 2 or more packs per day experienced nearly equal risks. Comparison of the most common cell types showed that women smokers had equal or lower ORs for squamous-cell carcinoma and adenocarcinoma, but higher OR for small-cell carcinoma, as compared with men smokers. While the smoking-associated OR were equal for small-cell and squamous-cell carcinomas in men, the OR for women were significantly higher for small-cell carcinoma than for squamous-cell carcinoma.