OBJECTIVES: Half of patients with systemic juvenile idiopathic arthritis (sJIA) will eventually fail to non-steroidal anti-inflammatory drugs (NSAIDs) or corticosteroids. Tocilizumab (TCZ) is indicated for patients with refractory sJIA. We aimed to determine the cost and the effectiveness of adding TCZ to conventional treatment for sJIA in Mexico. METHODS: We designed two decision models to compare TCZ versus placebo. In each model, two time horizons were analyzed: 12 weeks and one year. Target population consists of patients (2-19 years) with active sJIA and inadequate response to NSAIDs and corticosteroids. The dosing scheme for TCZ was based on body weight: 8 mg/kg for patients ≥30 kg and 12 mg/kg for patients <30 kg. The analysis was performed under the perspective of the public health care system in Mexico. Tocilizumab acquisition cost, infusion fees and standard management of sJIA according to level of response were evaluated. Efficacy was defined in terms of the American College of Rheumatology Pediatric response criteria. Resource use and unit costs were gathered from local sources; efficacy was derived from two phase-3 clinical trials; increase in mortality and utility scores associated with level of response was based on literature. All costs are expressed in 2011 euros (€). RESULTS: A markedly higher proportion of patients achieved an ACRPedi70 response with TCZ in both children with the possibility of maintaining methotrexate (71% vs. 8%) and in those without that alternative (75% vs. 13%). The incremental cost per achieving an ACRPedi70 response was around 2400€ in both models. During base-case, the incremental cost per Quality-Adjusted Life Year (QALY) gained with TCZ ranged from 10,636€ to 10,681€. The gross domestic product per capita in Mexico during 2010 was estimated at 7048€. Results were robust to variation in all parameters. CONCLUSIONS: TCZ is a cost-effective option to treat sJIA in Mexico.