Smoking is one of the most consistent epidemiological features related to occurrence and evolution of inflammatory bowel disease. Ulcerative colitis is accepted as a non or ex-smokers disease suggesting a protective role of tobacco against its development. In contrast there are more Crohn's disease cases between smokers. Sixty eight patients with inflammatory disease (36 ulcerative colitis; 32 Crohn's disease) and 136 patients with gastrointestinal functional disorders were matched for sex, age, scholarity and professional and religious patterns. They are divided in smokers, ex- and non-smokers. The inflammatory bowel disease patients were asked about the relationship between smoking and onset of the disease, and exposure, as passive smokers, during childhood. Smoking habit protected against ulcerative colitis (OR:0.30, IC:95%), but not against Crohn's disease (OR:0.81, P > 0.5). There was no increased risk for development of Crohn's disease between smokers; 72.7% of ex-smokers acquired ulcerative colitis and 44.4% Crohn's disease after tobacco habit has stopped. Exposure to environmental tobacco smoking during childhood did not increased the risk for ulcerative colitis (OR:0.93, P < 0.1) neither for Crohn's disease (OR:0.44, P < 0.2). Our results are similar to those of the literature related to protection of ulcerative colitis by smoking habit. Further experimental and clinic studies are in need to clarify the possible pharmacological and therapeutic action of tobacco products in this inflammatory disease.