Three siblings with acute sarcoid arthritis and hilar adenopathy on chest radiograph (Löfgren's syndrome) are presented. Synovianalysis from 2 of 3 showed a predominance of mononuclear cells, and synovial biopsies from 2 of the 3 showed a mild inflammatory synovitis. All 3 siblings exhibited the B8,DR3 phenotype, and HLA testing of 8 prior cases identified at this institution showed the B8,DR3 phenotype in 6 of 8 patients with the 2 other patients exhibiting either B8 or DR3 alone. We confirm an earlier report that the B8,DR3 phenotype identifies a group of patients who are more likely to have acute sarcoid arthritis and hilar adenopathy without developing chronic disease.