The two inflammatory bowel diseases (IBD), Ulcerative colitis CD and Crohn's disease UC are chronic relapsing diseases. As the major part of the health care costs of IBD consists of hospitalizations and surgery, there is a great potential for novel therapies to reduce costs and improve quality of life (QoL) if they could reduce the relapse rate and maintain patients in remission. A novel treatment option in these patients is the Granulocyte and monocyte/macrophage apheresis (Adacolumn®). OBJECTIVES: To estimate the cost-effectiveness of treating (CD) and (UC) patients with Adacolumn® aphaeresis compared to standard treatment. METHODS: We developed a Markov model for the treatment of UC and CD. The model and our cost-effectiveness application for CD and UC is based on four data sources: (a) an uncontrolled clinical study of the first 100 patients treated with Adacolumn® apheresis for IBD in clinical practice [The Scandinavian study], (b) a cohort of 147 IBD patients treated with usual care from Denmark [Danish Crohn Colitis Database-Copenhagen County) ] including 1 304 patient years (c) prices of health care and pharmaceuticals from Sweden, (d) and QALY data from literature. RESULTS: Surgical operations and days in hospital were reduced by 90 per cent. The cost per QALY gained by treating patients for three years with Adacolumn® is US$19,015 for UC and US$70,142 for CD, respectively. CONCLUSION: The comparison between the usual care treatment and the Adacolumn® treatment is based on the matching of two cohorts. Our results will be compared with forthcoming data from a randomized clinical trial. Compared to usual care Adacolumn® treatment of moderate severe UC and CD patients is associated with cost offsets for surgery, hospitalizations, outpatient care and drugs and an increase of QALYs. The cost-effectiveness ratios remain within the acceptable range for treatments to be recommended for use in Sweden.