Graves' disease is thought to be related to a defect in certain suppressor T-lymphocytes. It was of interest to discover Graves' disease in a 16 year old male with the DiGeorge syndrome. T-cell dysfunction had been documented in infancy by Kretschner, et. al (N. Engl. J. Med. 279:1295, 1968). Hyperthyroidism was documented and autoantibodies to thyroid microsomes were detected at age 13 years. Propylthiouracil treatment was begun. T-cell surface markers detected by monoclonal antibodies measured at age 14 years revealed OKT4, 34% and OKT8, 32%. After three years of antithyroid treatment, his immune status was reassessed; the number of circulating T cells (E-rosettes, 57%) and 3H-thymidine incorporation following exposure to phytohemag-glutinin (stimulation index (SI), 46:1) or candida (SI, 94:1) were normal.Although T-cell function now appears to be normal it is likely that defective thymic embryogenesis in the DiGeorge syndrome resulted in inadequate T suppressor cell development and allowed for the occurrence of Graves' disease. We propose that as more patients with congenital T cell defects survive, an increased frequency of autoimmune disorders, particularly those affecting the endocrine system, will be observed.