['Atopy and systemic onset juvenile idiopathic arthritis (SoJIA) are two potential outcomes of a dysregulated immune system. Although rare, SoJIA causes 60% of the morbidity of JIA patients which exhibit a wide heterogeneity of prognosis and treatment. Co-morbidities can complicate the responses to therapy.', 'To study the influence of co-existing atopy on the prognosis of SoJIA.', 'Patients diagnosed with SoJIA between Jan 2006 and Sep 2010 were screened, enrolled in this prospective cohort study, and followed for 2 years. Management of SoJIA patients was assessed by ACR Pedi30/50/70 criteria, laboratory variables, and systemic feature score.', 'At disease onset, 61 SoJIA patients (34 male and 27 female) were enrolled and were divided into SoJIA patients with atopy (n\u2009=\u200927) or those without atopy (n\u2009=\u200934). Atopic group at disease onset had significantly higher numbers of affected joints, ferritin levels and IgE serum levels than the non-atopic group. At 3 and 6 months, fewer SoJIA patients with atopy reached the ACR Pedi50 criteria (p\u2009<\u20090.02). During the 2 years of follow-up time, the number of infections and the number of flares were significantly higher in the SoJIA with atopy group (p\u2009<\u20090.01).'] Is atopy in children with systemic onset juvenile idiopathic arthritis ( SoJIA ) associated with a worse outcome?