Smoking is an important environmental factor in inflammatory bowel disease (IBD), having different effects in ulcerative colitis (UC) and Crohn's disease (CD). A recent meta-analysis partially confirmed previous findings that smoking was found to be p r o t e c t i v e a g a i n s t u l c e r a t i v e c o l i t i s a n d , a f t e r onset of the disease, might improve its course, d e c r e a s i n g t h e n e e d f o r c o l e c t o m y . H o w e v e r , smoking increases the risk of developing Crohn's disease and worsens its course, increasing the need for steroids, immunosuppressants and re-operations. Smoking cessation aggravates ulcerative colitis and improves Crohn's disease. Data are however, largely conflictive as well as the potential mechanisms involved in this dual relationship are still unknown. In this review article, the authors review the role of smoking in inflammatory bowel diseases.