To compare, in the Spanish setting, 2 drugs for adults with rheumatoid artritis (RA): leflunomide and subcutaneous methotrexate (SC). The high price of methotrexate SC compared with traditional presentations of methotrexate justifies conducting an economic evaluation comparing it with leflunomide. The analysis considered the annual costs of the drugs and their effectiveness, measured with a number needed to treat (NNT) approach, considering both the ACR20 and ACR50 criteria for effectiveness. Data about efficacy and dosage were derived from the clinical trial US310, a randomized, doble-blinded controlled trial, which compared efficacy and safety of leflunomide (20mg/daily) versus placebo versus methotrexate (7.5–15mg/weekly) in 482 patients with active RA. Data about use of medical resources for drug monitoring (visits to rheumatologists and diagnostic procedures) were derived from the manufacturerś summary of product characteristics. Direct costs (drugs and monitoring) were obtained from 2 Spanish databases. The analysis has been performed under the Spanish National Health System perspective. Using the ACR20 criteria, the NNT with leflunomide and methotrexate are 4 (95% CI, 2.56–7.71) and 5 (95% CI, 3.03–14.3) respectively. Using the ACR50 criteria, NNT are 4 (95% CI, 2.72-6.54) and 7 (95% CI, 4.03–19.3). In the case of leflunomide, annual treatment costs per patient-year equals €1793.30; in the case of methotrexate total treatment costs amounts to €2149.20 Combining these results the cost of a controlled patient according to ACR20 would amount €7173 for leflunomide and €10 746 for methotrexate SC. Results considering ACR50 are €7173 and €15 044 for leflunomide and methotrexate respectively. Comparar 2 farmacos para la artritis reumatoide (AR): leflunomida y metotrexato subcutaneo (s.c.) (jeringas precargadas), considerando tanto costes anuales de tratamiento como la efectividad medida a traves del numero de pacientes que es necesario tratar (NNT). Los datos de eficacia y dosis fueron extraidos del ensayo clinico US310, ensayo aleatorizado y doble ciego, que tuvo por objetivo comparar la eficacia y la seguridad del tratamiento a 12 meses con leflunomida (20mg/dia) frente a placebo y metotrexato (7,5–15mg/semana) en 482 pacientes con AR activa. La informacion sobre los actos medicos para los seguimientos de control se obtuvo de la ficha tecnica del producto. El estudio de costes se ha realizado con la perspectiva del Sistema Nacional de Salud espanol. Considerando el criterio de ACR20, el NNT de leflunomida es 4 (intervalo de confianza IC del 95%, 2,56-7,71) y el de metotrexato s.c., 5 (IC del 95%, 3,03–14,3); para el criterio de ACR50, el NNT de leflunomida es 4 (IC del 95%, 2,72–6,54) y el de metotrexato s.c., 7 (IC del 95%, 4,03–19,3). El coste anual del farmaco fue 1.112,52 euros para la leflunomida y 1.438,91 euros para el metotrexato s.c. Los costes anuales de monitorizacion fueron 680,76 euros para la leflunomida y 710,26 euros para el metotrexato s.c. Combinando la informacion, el coste de un paciente respondedor segun ACR20 seria de 7.173 euros con leflunomida y 10.746 euros con metotrexato s.c.; los resultados considerando ACR50 oscilarian entre los 7.173 euros para la leflunomida y 15.044 euros para el metotrexato s.c.