Patients (11) with arthritis complicating rubella were studied. The usual joints involved are the meta-carpophalangeal and proximal interphalangeal. The mean duration of arthritis was 9 days. Synovial fluid findings in 2 patients showed a pleocytosis of 14, 500 and 27, 000 leukocytes/mm3, with 90% or more polymorphonuclear cells. Synovial biopsy in 1 patient demonstrated a nonspecific active synovitis with synovial cell proliferation and inflammatory cell infiltration. All patients responded well to salicylate therapy and rest.