Previous epidemiologic studies have suggested a weak association between oral contraceptive use and Crohn's disease, specifically Crohn's colitis. To measure a possible etiologic association, 51 women with Crohn's disease who were 18-50 yr old were studied and compared with peer-nominated age- and sex-matched controls. There were no differences between cases and controls with respect to race, religion, marital status, and number of pregnancies. There was no association between oral contraceptive use and Crohn's disease incidence [current use: odds ratio (OR) 0.73, 95% confidence interval (CI) 0.34-1.59; former use: OR 1.80, CI 0.61-5.29; current or former use: OR 1.00, CI 0.46-2.16]. Stratifying by disease location also failed to identify an association. Cigarette smoking was significantly associated with Crohn's disease incidence. Controlling for possible confounding effects of cigarette smoking did not alter the lack of association between oral contraceptive use and Crohn's disease. Similarly, testing for interaction failed to demonstrate any effect modification. Analyzing for duration of current oral contraceptive use or time interval since last use failed to demonstrate a "dose-response" effect. The study was of sufficient size to detect statistical significance for oral contraceptive use for odds ratios of greater than or equal to 2.76. From this community-based matched case-control study, there was no association between oral contraceptive use and Crohn's disease, and women need not be advised to discontinue oral contraceptive use when a diagnosis of Crohn's disease is made.