- Background The association between smoking and inflammatory bowel disease (IBD) is well established. There are, however, no large scale studies of passive smoking in inflammatory bowel disease and this has never been surveyed in the Jewish population of Israel. Aim To study the passive smoking exposure of Jewish IBD patients in Israel in a large scale multicentre study. Methods Patients with established IBD, aged 18-70 years, were interviewed regarding smoking and other habits. Two controls, one clinic and one neighbourhood, matched by age, sex, community group, and education, were sought for each subject. Results Five hundred and thirty-four patients (273 ulcerative colitis (UC) and 261 Crohn's disease (CD)), 478 clinic controls and 430 community controls were interviewed. There were no significant differences in the passive smoking habits between IBD patients and their controls. Fifty-one percent of UC patients, 50% of the clinic controls and 58% of the community controls were exposed to passive smoking at home (NS); similar results were found among CD patients (50%, 55% and 56%, respectively). When a quantitative exposure index was used UC patients were significantly less exposed to passive smoking than were their community controls (7.46 ± 8.40 vs 9.36 ± 9.46, n = 229, P< 0.031). There was no difference in the exposure to passive smoking among CD patients and their controls. No differences in exposure to passive smoking were found when UC patients who had never smoked were compared with their controls. When the quantitative index was used 'never-smoked' CD patients tended to be less exposed to passive smoking at home than their community controls (5.40 ± 7.60 vs 8.04 ± 8.72, P < 0.05). Conclusion There is a lack of association between passive smoking and IBD in Jewish patients in Israel. When a quantitative exposure index was used UC patients were found to be less exposed to passive smoking than their community controls.