Abstract Three patients are described with clinical features of connective tissue diseases, namely, dermatomyositis, progressive systemic scleroderma, and systemic lupus erythematosus. In two patients the symptoms of disease overlapped. The rare anti-Ku antibody was found in all of them. Anti-Ku antibody characterizes those patients with polymyositis-scleroderma overlap syndromes who have a good prognosis. One of our patients, who also had severe anti-Sm-positive systemic lupus erythematosus, seems to be an exception.