A 5-year-old boy presented with fever, rash, lymphadenopathy and polyarthritis. Systemic onset juvenile idiopathic arthritis was initially considered in the differential diagnosis, but lymph node biopsy established the diagnosis of Rosai-Dorfman disease (RDD). The arthritis recurred twice. Both times it correlated with the severity of the other clinical and laboratory abnormalities of RDD and responded to treatment with dexamethasone and vinblastine. This report adds inflammatory arthritis to the extranodal manifestations of RDD in children and suggests that this disorder should be considered as a rare cause of fever with rash, lymphadenopathy and arthritis.