Four adults with an illness similar to the systemic variant of juvenile rheumatoid arthritis seen in children (Still's disease) are described. All four had fever, an erythematous maculopapular rash, splenomegaly and arthritis. The arthritis was asymmetric and involved only a few joints simultaneously. Erosive arthritis developed in one patient. Three patients had a sore throat, two had pleurisy and pericarditis, and one had transient abnormalities of liver function. The laboratory features included anemia, leukocytosis and high leukocyte counts in the synovial fluid. High titres of rubella hemagglutination-inhibiting antibody were detected in two patients, one of whom was found to have rubella virus in the urine. Only one patient responded well to therapy with acetylsalicylic acid; the other three were given prednisone therapy, and two continue to require it.