OBJECTIVES: Bulimia nervosa (BN) is characterised by recurrent episodes of binge eating and secondly by compensatory behaviour to prevent weight gain. Its prevalence has been estimated between 0.5% and 1.0% in young women. A recent clinical guideline was commissioned to establish the optimum clinical management of BN in the UK. Antidepressants and bulimia nervosa specific cognitive behaviour therapy (CBT-BN) were identified as the leading pharmacological and psychological therapies in the clinical review. This study reports the results of the cost-effectiveness analysis of these strategies conducted as part of the guideline development process. METHODS: A decision analytic model was developed to calculate the incremental cost-effectiveness of antidepressant therapy (fluoxetine), CBT-BN and their combination from the NHS's viewpoint. Remission data were obtained from the guideline meta-analyses, resource use data were collected from the literature and experts. Unit costs were calculated for year 2002/03. Different baseline scenarios and uncertainty around the estimates (probabilistic analysis) were explored. RESULTS: Combination therapy is dominated by the other two strategies and was excluded from the final calculation. CBT-BN is more effective and has higher treatment costs than fluoxetine prescribed in primary care with an incremental cost-effectiveness ratio (ICER) of £4,807. The probability of CBT-BN being cost-effective is 50% if decision makers are willing to pay between £4,000-£5,000 for an additional successfully treated BN case, but it increases to approximately 95% if the threshold value is £10,000. CONCLUSIONS: Significant uncertainty around these results still exists (e.g. the true cost of side effects of antidepressant therapy are unknown, nor have attempts been made to quantify possible costs averted due to successful treatment). When further research is carried out, it will be necessary to re-estimate the cost-effectiveness of each alternative incorporating such influences. However, all these influences are likely to favour CBT-BN and so, current estimates may be considered conservative.