Reticulohistiocytoma is a seldom recognized but serious condition of unknown etiology involving the skin, often with destructive changes in joints, bones, and synovial membranes accompanied by histiocytic reactions. The lesions in the skin precede the destructive changes in the joints, synovial membranes, and bones. Johnson and Tilden,1 under the title "Reticulohistiocytic Granulomas of the Skin Associated with Arthritis Mutilans," have recently presented a case and thoroughly reviewed the literature. We wish to report in greater detail (Kierland2 and Montgomery3) the subsequent course of two patients whom we have seen at the Mayo Clinic and also to attempt to clarify, in part, the confusion in terminology regarding this condition, as indicated by the report of Davies and Wood.4 Caro and Senear,5 under the title "Reticulohistiocytoma of the Skin," reported two cases in which they thought rheumatoid arthritis was associated. Caro personally