The characteristic rash of systemic juvenile idiopathic arthritis is a transient erythematous eruption associated with a quotidian spiking fever. Usually asymptomatic, it can be pruritic, with dermatographism at sites of scratching or pressure. An illness similar to this entity in adults is designated adult-onset Still disease. The relationship between the pediatric and adult disease is uncertain and differences in case definition have evolved. Specifically, a sustained arthritis for at least 6 weeks is required for a diagnosis of systemic juvenile idiopathic arthritis, whereas transient arthritis and arthralgia are accepted criteria in adult-onset Still disease. We describe five patients less than 16 years of age who presented with an acute illness characterized by fever and a distinctive skin eruption. Intense pruritus and linear erythematous lesions flared with a spiking fever, usually in the late afternoon and evening. Periorbital edema/erythema and nonlinear urticarial lesions were also seen. Two children had splinter hemorrhages of the nail beds and one girl developed a fixed, scaling, pigmented, linear eruption. Severe malaise, myalgia, arthralgia, and leukocytosis were present in every patient. Other systemic manifestations included sore throat, transient arthritis, abdominal pain, lymphadenopathy, hepatomegaly, splenomegaly, hyperferritinemia, and hepatic dysfunction. No patient had a sustained arthritis. The course of the disease was variable. One patient, diagnosed with macrophage activation syndrome, recovered on oral naproxen. Two patients responded to systemic corticosteroid therapy. One girl developed status epilepticus and died from aspiration and asphyxia. A boy with severe hepatitis developed renal failure and thrombotic thrombocytopenic purpura and was treated with plasmapheresis, dialysis, and systemic corticosteroids; he had recurrent episodes of rash and fever into adult life. These children did not fulfill the case definition of systemic juvenile idiopathic arthritis because they lacked a persistent arthritis. Adolescent and adult patients with the same clinical and laboratory findings are described under the rubric of adult-onset Still disease. Recognition of the distinctive urticarial skin eruption and spiking fever is important in the diagnosis of a disease with severe morbidity and potentially life-threatening complications.