A case-control study of 480 patients with invasive cervical cancer and 797 population controls, conducted in five geographic areas in the United States, included an evaluation of the relationship of several cigarette smoking variables to cervical cancer risk. Although smoking was correlated with both age at first intercourse and number of sexual partners, a significant smoking-related risk persisted for squamous cell carcinoma after adjustment for these factors (relative risk, 1.5). The risk of squamous cell cancers increased significantly with intensity and duration of smoking. Twofold excess risks were seen for those smoking 40 or more cigarettes per day and those smoking for 40 or more years. In addition, users of nonfilter cigarettes were at particularly high risk. Increased risks, however, were observed only among recent and continuous smokers. In contrast to squamous cell cancer, no relationship was observed between smoking and risk of adenocarcinoma or adenosquamous carcinoma (n=63). These results suggest a causal relationship between cigarette smoking and invasive squamous cell cervical cancer, perhaps through a late-stage or promotional event, although the mechanisms of action require further elucidation.