Two thirds of patients with juvenile idiopathic arthritis (JIA) treated with tumor necrosis factor (TNF)-alpha inhibitors respond initially, but only about one third of patients achieve clinical remission at follow-up. We evaluated the 1-year response and long-term treatment adherence to TNF inhibitor treatment in JIA patients naive to biologics and investigated if baseline myeloid-related protein (MRP)-8/14 and C-reactive protein (CRP) were predictive of treatment response. One hundred fifty-two patients were included in a unicenter observational, prospective study from 2002 to 2015, excluding patients with systemic-onset JIA. One-year treatment response was evaluated by American College of Rheumatology-pediatric (ACR-ped) and by the number of patients achieving inactive disease (ID). Medical charts were reviewed for reasons of treatment withdrawal. After one year of treatment ACR-ped 30, 50, 70, and 90 were achieved by 61, 55, 38, and 10 % of the patients, and 23 % achieved a status of ID. Treatment adherence: 51 % withdrew from treatment due to lack of clinical effect, while 32 % continued treatment or withdrew due to disease remission. Increased MRP-8/14 concentrations at treatment initiation was associated with ID after 1 year (OR 1.55, CI 1.06–2.25, p = 0.02). Treatment withdrawal due to lack of effect was associated with low baseline levels of both MRP-8/14 (685 vs. 1235 ng/ml, p < 0.001) and CRP (0.75 vs. 2.73 mg/l, p < 0.001), verified by multivariable logistic regression analysis (OR 0.51, CI 0.34–0.77/OR 0.63, CI 0.48–0.83). In conclusion, an association was found between ID after 1 year of treatment and increased baseline levels of MRP-8/14. Furthermore, low baseline MRP-8/14 and CRP concentrations were associated with treatment withdrawal due to lack of clinical effect.