OBJECTIVE: This study was undertaken to evaluate the long-term safety and effectiveness of etanercept alone or in combination with methotrexate (MTX) in children with selected categories of juvenile idiopathic arthritis (JIA). METHODS: Patients ages 2-18 years with rheumatoid factor (RF)-positive or RF-negative polyarthritis, systemic JIA, or extended oligoarthritis were eligible for the study. Patients received MTX alone (> or =10 mg/m(2)/week [ approximately 0.3 mg/kg/week], maximum dosage 1 mg/kg/week), etanercept alone (0.8 mg/kg/week, maximum dose 50 mg), or etanercept plus MTX for 3 years in an open-label, nonrandomized study. Safety was assessed by measuring rates of adverse events, and effectiveness was assessed using the physician's global assessment of disease activity and the pediatric total joint assessment. RESULTS: A total of 197, 103, and 294 patients were enrolled in the MTX, etanercept, and etanercept plus MTX groups, respectively. Exposure-adjusted rates of adverse events were similar among the 3 treatment groups (18.3, 18.7, and 21.6 per 100 patient-years in the MTX, etanercept, and etanercept plus MTX groups, respectively). Respective rates per 100 patient-years of serious adverse events (4.6, 7.1, and 6.0) and medically important infections (1.3, 1.8, and 2.1) were also similar among the 3 treatment groups. Scores for physician's global assessment and total active joints improved from baseline, and improvement was maintained for the duration of the study. CONCLUSION: These data confirm the findings of other long-term studies and suggest that etanercept or etanercept plus MTX has an acceptable safety and effectiveness profile in children with selected categories of JIA. Improvement was maintained for 3 years in those continuing to receive medication.