Abstract Background: Evaluation of costs and short-term cost-effectiveness of infliximab plus methotrexate (IFX + MTX); triple therapy of hydroxychloquine, sulphasalazine, and methotrexate (TRIPLE); or methotrexate monotherapy (MTX) in patients with new-onset polyarticular juvenile idiopathic arthritis (JIA). Methods: In a prospective multicenter study (ACUTE-JIA), costs and health outcomes of 60 randomized patients with new-onset disease-modifying anti-rheumatic drug (DMARD)-naïve polyarticular JIA were analyzed during the first year. A mapping algorithm was used to obtain utility values from Child Health Assessment Questionnaire (CHAQ). Wallace criteriae were used to assess clinically inactive disease (CID). Linear regression with non-parametric bootstrapping was used to adjust imbalances at baseline. Results: Using prices for IFX biosimilar, adjusted annual mean (SD) costs of treatment (€) were 21,164 (4158), 12,136 (5286), and 18,300 (8635) on IFX + MTX, TRIPLE, and MTX, respectively. Incremental cost-effectiveness ratio (ICER) for IFX + MTX as compared with TRIPLE or MTX were 3442 € or 678 € per additional month spent in CID. Mean (SD) quality-adjusted life years (QALYs) for IFX + MTX, TRIPLE and MTX were 0.755 (0.065), 0.725 (0.062), and 0.686 (0.124). ICER for IFX + MTX vs TRIPLE was 294,433 €, and for IFX + MTX vs MTX 31,435 € per QALY gained. Conclusions: In short-term, biosimilar IFX + MTX can be considered cost-effective when compared with MTX alone. TRIPLE was cost-effective when compared with MTX and showed cost advantage when compared with IFX + MTX. Cost per time spent in CID showed similar results than ICER evaluations. Trial registration: This trial was primarily registered with the Ethical Board of Helsinki District University Hospital (https://www.hus.fi), clinical trial number 211864, and later with ClinicalTrials.gov, number NCT01015547.