BACKGROUND: Cigarette smoking is associated with a more severe Crohn's disease (CD) course. However, the effect of light consumption is not known. Our aim was to characterize the effect of a light tobacco consumption on the course of CD. METHODS: We analyzed the course of CD during the period 1995-2007 from data collected in 2795 consecutive patients in whom smoking habits were recorded. Patients were classified as nonsmokers (n = 1420), light smokers (1-10 cigarettes/day; n = 385), heavy smokers (>10 cigarettes/day; n = 638), and intermittent smokers (change in smoking habits; n = 352). Patient-years while smoking were compared to patient-years without smoking. The analyses considered patient-years regarding annual disease activity and therapeutic requirements. RESULTS: The percentage of years with active disease was 37% in nonsmokers versus 46% in light smokers (P < 0.001; adjusted hazard ratio 1.30 [1.19-1.43]) and 48% in heavy smokers (P < 0.001; adjusted hazard ratio 1.68 [1.57-1.81]), despite an increased use of immunosuppressants in smokers. Hospitalization rates were also increased in both groups of smokers, with 12% in nonsmokers versus 15% in both groups of smokers (P < 0.001 for both comparisons). The annual rate of intestinal resection was 4.5% in nonsmokers, 5.1% in light smokers, and 5.5% in heavy smokers, with a significant difference observed between nonsmokers and heavy smokers only (P < 0.01). CONCLUSIONS: Light smokers are doing worse than nonsmokers regarding disease activity and the need for immunosuppressants. Complete smoking cessation should be advised in all smokers with CD.