Descriptive surveys of the epidemiology of inflammatory bowel disease from the north and south of Europe show north-south gradient in its incidence and continue to point to lifestyle and environmental causes. This theme is further examined in studies of the causal association between inflammatory bowel disease and smoking, oral contraceptive use, and diet by investigators from the United States and Europe, but the results are not conclusive. Childhood exposure to environmental tobacco smoke and the risk of ulcerative colitis is a new entry to the field that shows decreased risk of ulcerative colitis in passive smokers.