Background and Aims: Smoking affects the course of inflammatory bowel disease [IBD]. We aimed to study the impact of smoking on IBD-specific costs and health-related quality-of-life [HrQoL] among adults with Crohn's disease [CD] and ulcerative colitis [UC]. Methods: A large cohort of IBD patients was prospectively followed during 1 year using 3-monthly questionnaires on smoking status, health resources, disease activity and HrQoL. Costs were calculated by multiplying used resources with corresponding unit prices. Healthcare costs, patient costs, productivity losses, disease course items and HrQoL were compared between smokers, never-smokers and ex-smokers, adjusted for potential confounders. Results: In total, 3030 patients [1558 CD, 1054 UC, 418 IBD-unknown] were enrolled; 16% smoked at baseline. In CD, disease course was more severe among smokers. Smoking was associated with >30% higher annual societal costs in IBD ((sic) 7,905 [95% confidence interval (sic) 6,234 -(sic) 9,864] vs (sic) 6,017 [(sic) 5,186 -(sic) 6,946] in never-smokers and (sic) 5,710 [(sic) 4,687 -(sic) 6,878] in ex-smokers, p = 0.06 and p = 0.04, respectively). In CD, smoking patients generated the highest societal costs, primarily driven by the use of anti-tumour necrosis factor compounds. In UC, societal costs of smoking patients were comparable to those of non-smokers. Societal costs of IBD patients who quitted smoking >5 years before inclusion were lower than in patients who quitted within the past 5 years ((sic) 5,135 [95% CI (sic) 4,122 -(sic) 6,303] vs (sic) 9,342 [(sic) 6,010 -(sic) 12,788], p = 0.01). In both CD and UC, smoking was associated with a lower HrQoL. Conclusions: Smoking is associated with higher societal costs and lower HrQoL in IBD patients. Smoking cessation may result in considerably lower societal costs.