We used rosters of the Crohn's and Colitis Foundation of America to identify potential cases and peer-nominated controls to explore the reported association between oral contraceptives and inflammatory bowel disease. Overall, women who used oral contraceptives were at increased risk of developing Crohn's disease (odds ratio = 1.49, 95% confidence interval (CI) = 0.99-2.26). The findings persisted after adjustment for age at symptom onset, decade of onset, education, marital status, and location of disease. There was an interaction with cigarette smoking; the risk associated with oral contraceptives was elevated in current smokers (odds ratio = 2.64, 95% CI = 1.22-5.75), but not in former smokers or never-smokers. The risk was not elevated for ulcerative colitis (odds ratio = 1.10, 95% CI = 0.65-1.85).