Seven children with juvenile rheumatoid arthritis had a syndrome characterized by hemorrhage and neurologic, hepatic, hematologic, and metabolic manifestations. The disease did not seem to conform clearly to the characteristics of Reye syndrome or any other well-known entity. This severe complication may be induced by macrophage activation secondary to a drug or intercurrent infection. Our data suggest that a sudden fall in erythrocyte sedimentation rate or in platelet and fibrinogen levels may mark the start of this complication and may be an indication for rapid steroid therapy.