BACKGROUND: It is controversial whether CARD15 variants are truly associated with a more severe form of Crohn's disease. The relative role of CARD15 genotype and smoking in Crohn's disease progression is also debated. AIM: To investigate the association between CARD15 variants and history of resective surgery in patients with Crohn's ileal disease, taking into account smoking as a possible confounding factor. METHODS: We originally assessed CARD15 genotype in 239 north Italian Crohn's disease patients (mean follow-up: 10.1 +/- 8.1 years). We then focused on 193 patients with proven ileal involvement, 70 of whom (36.3%) carried CARD15-mutated alleles (G908R, R702W, L1007fs). RESULTS: Carriage of CARD15 variants was positively associated with family history and ileal-only disease and negatively associated with uncomplicated behaviour at maximal follow-up (P < 0.05). Ileal resection was the only variable independently associated with CARD15 variants at multivariate analysis (OR 3.8; 95% CI 1.6-9.2; P = 0.003). Kaplan-Meier analysis showed that ileal resection was favoured both by CARD15 variant-carriage (P = 0.01) and by smoking (P = 0.05), but smoking did not affect progression to surgery in variant carriers (P = 0.31). Thirteen of 14 (93%) patients being resection-free at 15-year follow-up, had CARD15 wild-type genotype (P = 0.01), whereas only seven (50%) had never smoked (P = 1.0). CONCLUSIONS: In summary, CARD15 variant-associated Crohn's ileitis is virtually committed to stricturing and/or penetrating disease and, eventually, to resective surgery. Smoking accelerates progression to surgery in patients with wild-type CARD15 genotype, but it seems to exert no additional effect in CARD15-variant carriers.