In this study, we evaluate the distribution of nitric oxide (NO) in the serum of juvenile idiopathic arthritis (JIA) patients, correlating it with parameters of the severity of the disease. Ninety-seven patients with mean age 11.7 years and disease duration 4.8 years, showing active disease or not, grouped as oligoarticular (n = 34), polyarticular (n = 29) and systemic (n = 34) group, presenting uveitis and positive RF with erosive arthritis or active disease and erosions had significantly high levels of NO than the inactive ones. NO correlated with TNF-alpha in the oligoarticular subtype (P < 0.03), with pain in the polyarticular subtype with active disease (P < 0.04) and with ESR in the systemic subtype with active disease (P < 0.03). TNF-alpha concentration was high in all patients with active disease, accompanying NO production. The data confirm the production of NO in JIA patients, indicating a possible positive correlation between the production of NO and severity of the disease.