[Epidemiology of inflammatory bowel disease: controversies in classical epidemiology]

Incidence and prevalence of inflammatory bowel diseases (IBD) have shown a dramatic increase in last decades. Diagnosis can be made at any age, no sex predominance is apparent, and while mortality rates are similar to in general population, higher rates of colorec-tal cancer are evident in most studies, probably as a consequence of long-term chronic inflammation. Probably, IBD are polygenic diseases sharing genes of sus-ceptibility for both of them (Ulcerative colitis and Crohn disease), but with other specific different genes for each one. Among environmental risk factors described, smoking is the most important, with different behaviour in both diseases, though there have been described other associated risk factors like appendectomy, oral contraceptives, infections, diet, childhood hygiene, and non-steroidal anti-inflammatory intake.