Thymic carcinoma is exceptionally rare in children and it has never previously been associated with autoimmune disorders. The authors report the case of an 11-year-old boy with thymic carcinoma, hypertrophic pulmonary osteoarthropathy, and an autoimmune disease that resembled systemic lupus erythematosus. To their knowledge, this is the first case of such complex clinical findings. The tumor was of high grade histologically and the boy died after 1 year, in spite of chemotherapy and radiotherapy. A review is presented of the available medical literature on thymic malignancy in childhood.