Rheumatoid synovial cyst of the hip apparently is a rare developnment in the course of a relatively common disease. The occurrence of rheumatoid synovial cysts of the hips in three patients with extensive chronic rheumatoid arthritis of fifteen or more years' duration is described. Theories as to pathogenesis of this condition, the differential diagnosis of inguinal masses, and the treatment of rheumatoid synovial cysts in the inguinal region are discussed.