OBJECTIVES: To assess whether circulating levels of 90K glycoprotein are increased in children with juvenile idiopathic arthritis (JIA) at different stages of the disease, compared to healthy controls and to evaluate potential over time changes in its concentrations following treatment with the antitumor-necrosis factor (TNF) drug etanercept. METHODS: 90K glycoprotein, C-reactive protein, erythrocyte sedimentation rate, TNF, antinuclear antibodies, rheumatoid factor and the Juvenile Arthritis Disease Activity Score were assessed in 71 children: 23 with newly diagnosed JIA, 23 with established and active JIA and 25 healthy controls. Patients, eligible for anti-TNF treatment, underwent a similar clinical/laboratory assessment after 6- and 12-month etanercept therapy. RESULTS: At baseline, significant differences were found in 90K levels between the three study groups: JIA at onset (157.7 [131.4-241.5] μg/ml), JIA on treatment (90.0 [68.8-120.2] μg/ml) and control group (58.0 [44.5-79.0] μg/ml), (p for trend <.001), with the JIA at onset group showing the highest values. In the JIA on treatment group, following one-year etanercept treatment, a significant reduction in 90K was detected already at 6 months (74.3 [56.0-104.1] μg/ml p = .001) and a further decline was observed at 12 months (49.3 [46.0-67.6] μg/ml p < .001). CONCLUSION: Our study showed that 90K glycoprotein levels are increased in JIA children compared to healthy controls, suggesting a potential pathogenetic role in the JIA. Besides, 12 months of therapy with etanercept can reduce 90K levels.