Background: Treatment with tumour necrosis factor (TNF)-alpha inhibitors offers promising new opportunities to improve the health-related QOL of patients with rheumatoid arthritis (RA) in Denmark. As of September 2003, two such compounds - infliximab and etanercept - were registered for use by patients with RA. These drugs have shown the ability to reduce disease activity and to slow down or halt the development of new joint damage in otherwise treatment-resistant patients with RA. The acquisition cost of the drugs is high, with I year of treatment costing EURO9000-12000 per patient. Objective: The aim of this study was to assess the potential impact on the Danish healthcare budget of prescribing infliximab or etanercept to patients with RA. Method: Two treatment implementation scenarios were investigated. In the progressive scenario, all patients newly diagnosed with RA were offered TNF alpha inhibitors as the drug of first choice. In the modest scenario, only patients with insufficient disease suppression by conventional therapy with disease-modifying anti-rheumatic drugs (DMARDs) were offered TNF alpha inhibitor therapy. The budget impact analysis, which was part of a Danish health technology assessment of TNF alpha inhibitors, focused on the number of patients offered treatment during a 5-year period and resource use related to drug and staff costs. Simple sensitivity analyses assessed the consequences of changing the drug dosage, the number of patients offered treatment and the rate of treatment cessation. Results: The results suggested that both implementation strategies would impose additional costs per year on the Danish healthcare service, in the range of EURO67-188 million for the progressive scenario and EURO17-49 million for the modest scenario (price level August 2002). These costs represent between half and up to five times the amount currently used on treating patients with RA. Conclusion: This analysis suggests that the introduction of TNF alpha inhibitors into the treatment regimen of patients with RA could pose a considerable financial burden on the Danish healthcare system.