A 31-year-old male patient complaining of repeated respiratory infections was revealed to be in an immunodeficient state in both humoral and cellular immunity and accompanied by dermatomyositis which was proved by both clinical and histological findings. Persistent diarrhea followed by colonic bleeding due to multiple ulcers and a severe liver dysfunction seemed to bring him to his death. The autopsy revealed the presence of thymoma of spindle cell type, depleted cells in the systemic lymphatic systems and inflammatory lesions in the muscle, liver, lung, kidney and gastrointestinal tract. This is the first report of Good's syndrome accompanied by dermatomyositis.