AbstractA 31‐year‐old black woman was studied who, at the age of 12 years, underwent splenectomy for a bleeding disorder due to idiopathic thrombocytopenic purpura (ITP). More than 20 years after the first signs of her bleeding disorder, the patient developed signs of Graves disease. This condition was treated with131I with resulting hypothyroidism. The rare combination of ITP and Graves disease was considered to be a manifestation of two separate autoimmune diseases. For the second time in the literature, HLA typing was performed in a patient with such a disease combination, and it was found to be of the group A23, A28, and B17. This is different from B8, which is most frequently found in both isolated ITP and Graves disease. Possible racial factors may be involved. It is concluded that more cases of such combined disease need to be studied before possible genetic patterns can be establis