This paper presents a summary of the evidence review group (ERG) report into the clinical effectiveness and cost-effectiveness of infliximab for the treatment of acute exacerbations of ulcerative colitis, in accordance with the licensed indication, based upon the manufacturer's submission to the National Institute for Health and Clinical Excellence (NICE) as part of the single technology appraisal process. The submitted clinical evidence included four randomised controlled trials (RCTs), two comparing infliximab with placebo in patients not responsive to initial treatment with intravenous corticosteroids and one comparing ciclosporin with placebo. A fourth RCT compared ciclosporin with intravenous corticosteroids as the initial treatment after hospitalisation. The manufacturer's submission concluded that infliximab provides clinical benefit to patients with acute severe, steroid-refractory ulcerative colitis and is well tolerated; it also provides additional clinical benefits over ciclosporin, particularly avoidance of colectomy. A decision tree model was built to compare infliximab with strategies involving ciclosporin, standard care and surgery. After correcting a small number of errors in the model, the revised base-case incremental cost-effectiveness ratio (ICER) for infliximab compared with standard care was 20,000 pounds. However, sensitivity analyses revealed considerable uncertainty emanating from the weight of the patient, the timeframe considered and, most importantly, the colectomy rates used. When a more appropriate mix of trials were included in the estimation of colectomy rates, the ICER for infliximab rose to 48,000 pounds. The guidance issued by NICE on 31 October 2008 states that infliximab is recommended as an option for the treatment of acute exacerbations of severely active ulcerative colitis only in patients in whom ciclosporin is contraindicated or clinically inappropriate, based on a careful assessment of the risks and benefits of treatment in the individual patient; for people who do not meet this criterion, infliximab should only be used for the treatment of acute exacerbations of severely active ulcerative colitis in clinical trials.