Background: Environmental exposures in early life have been implicated in the aetiology of inflammatory bowel disease. Objective: To examine environmental ri sk factors prior to the development of inflammatory bowel disease in a paediatri c population based case control study. Methods: A total of 222 incident cases of Crohn’ s disease and 60 incident cases of ulcerative colitis occurring before 17 years of age between January 1988 and December 1997 were matched with one con trol subject by sex, age, and geographical location. We recorded 140 study varia bles in a questionnaire that covered familial history of inflammatory bowel dise ase, events during the perinatal period, infant and child diet, vaccinations and childhood diseases, household amenities, and the family’ s socioeconomic statu s. Results: In a multivariate model, familial history of inflammatory bowel dise ase (odds ratio (OR) 4.3 (95% confidence interval 2.3- 8)), breast feeding (O R 2.1 (1.3- 3.4)), bacille Calmette- Guerin vaccination (OR 3.6 (1.1- 11.9)), and history of eczema (OR 2.1 (1- 4.5)) were significant risk factors for Croh n’ s disease whereas regular drinking of tap water was a protective factor (OR 0.56 (0.3- 1)). Familial history of inflammatory bowel disease (OR 12.5 (2.2- 71.4)), disease during pregnancy (OR 8.9 (1.5- 52)), and bedroom sharing (OR 7. 1 (1.9- 27.4)) were risk factors for ulcerative colitis whereas appendicectomy was a protective factor (OR 0.06 (0.01- 0.36)) . Conclusions: While family hist ory and appendicectomy are known risk factors, changes in risk based on domestic promiscuity, certain vaccinations, and dietary factorsmay provide new aetiologi cal clues. Background: Environmental exposures in early life have been implicated in the aetiology of inflammatory bowel disease. Objective: To examine environmental ri sk factors prior to the development of inflammatory bowel disease in a paediatri c population based case control study. Methods: A total of 222 incident cases of Crohn’s disease and 60 incident cases of ulcerative colitis occurring before 17 years of age between January 1988 and December 1997 were matched with one con trol subject by sex, age, and geographical location. We recorded 140 study varia bles in a questionnaire that covered familial history of inflammatory bowel disese, events during the perinatal period, infant and child diet, vaccinations and childhood diseases, household amenities, and the family’s socioeconomic stats. Results: In a multivariate model, familial history of inflammatory bowel dise ase odds ratio 4.3 (95% confidence interval 2.3-8), breast feeding (OR 2.1 (1.3- 3.4)), bacille Calmette-Gue rin vaccination (OR 3.6 (1.1-11.9)), and history of eczema (OR 2.1 (1- 4.5)) were significant risk factors for Croh n ’s disease were regular drinking of tap water was a protective factor (OR 0.56 (0.3 - 1)). Familial history of inflammatory bowel disease (OR 12.5 (2.2-71.4)), disease during pregnancy (OR 8.9 (1.5- 52)), and bedroom sharing Factors for ulcerative colitis and appendicectomy were a protective factor (OR 0.06 (0.01-0.36)). Conclusions: While family histories and appendicectomy are known risk factors, changes in risk based on domestic promiscuity, certain vaccinations, and dietary factors may provide new aetiologi cal clues.