Abstract A 65-year-old woman with a history of primary biliary cirrhosis was diagnosed as having myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA)-associated crescentic glomerulonephritis (GN) during propylthiouracil (PTU) therapy for Graves' disease. Antinuclear antibodies, as well as various thyroid-associated autoantibodies, had been detected since the diagnosis of Graves' disease was made. The patient carried human leukocyte antigens (HLAs) DR4 and DR9, the two HLA haplotypes that have been reported to be related to ANCA-associated vasculitis. Withdrawal of PTU and the administration of prednisolone resulted in a decrease in the titer of MPO-ANCA, together with an improvement in renal function. It is suggested that in addition to the PTU therapy, her genetic predisposition to autoimmunity had played a role in the production of MPO-ANCA and the development of crescentic GN.