OBJECTIVES: To evaluate the cost-effectiveness of monotherapy TCZ in DMARD-IR patients intolerant of or contraindicated to MTX in the United Kingdom (UK). METHODS: An economic model was developed to reflect the healthcare system and treatment pathway in the UK. In the model, disease severity is represented by the health assessment questionnaire (HAQ) score; a surrogate health outcome which can be translated to utility scores and ultimately quality adjusted life years (QALYs). The model captures the progression of the HAQ score for each individual patient. Benefits were expressed as QALYs. Costs were calculated from a National Health Service and Personal Social Services perspective. The analysis calculated incremental costs and benefits associated with the addition of TCZ in first line to the standard care pathway involving certolizumab pegol, etanercept and adalimumab. Efficacy data for comparator biologic monotherapies were available from monotherapy trials of adalimumab (van de Putte et al 2004), certolizumab pegol (Fleischmann et al 2009), and etanercept (Moreland et al 1999). TCZ efficacy was informed by results from the ADACTA study (Gabay et al 2012), a new head-to-head superiority trial of TCZ and adalimumab monotherapy in RA. The economic model used inputs derived through a mixed treatment comparison that indirectly compared TCZ monotherapy with the standard of care biologic monotherapy treatments used in the UK (Roche data on file). RESULTS: Base case results estimated incremental costs of approximately £20,230 and incremental QALYs of 0.88. The incremental cost-effectiveness ratio (ICER) was £22,950 per QALY gained. A probabilistic sensitivity analysis produced a very similar ICER of £23,200 per QALY gained. CONCLUSIONS: The results of this analysis suggest that TCZ monotherapy represents an efficacious and cost-effective addition to the current standard of care in the United Kingdom, for treating RA patients who are intolerant of or contraindicated to MTX.