The connection between smoking and cervical neoplasia has been questioned. The association demonstrated has been suspected to depend on a correlation between smoking and sexual behavior or other risk factors for cervical neoplasia. This case-control study included 140 women with cervical intraepithelial neoplasia diagnosed during pregnancy. For each case, 2 healthy, age-matched women, who simultaneously attended for a pregnancy check at the same maternity clinic, served as controls. Information was obtained on obstetrical and gynecological history, sexual behavior, contraceptive methods, female and male smoking habits and socioeconomic status, using both an interview and a questionnaire. The patients were significantly younger at first intercourse and first pregnancy, had more sexual partners, showed a higher frequency of both female and male smokers and had a different pattern of contraceptive use vis-á-vis the controls. Analyses of covariance were used to identify and check for possible confounding before a log-linear regression analysis was ultimately carried out. Two factors remained closely associated with cervical intraepithelial neoplasia: number of sexual partners, and female smoking. We conclude that smoking seems to be a genuine risk factor for cervical intraepithelial neoplasia.