A patient with primary biliary cirrhosis had a dramatic deterioration in liver function with jaundice over 2 months as a result of development of Graves' disease. Clinical examination and radiological and cardiovascular investigations excluded heart failure and biliary obstruction as the cause of this deterioration. The patient's jaundice entirely reversed with treatment of hyperthyroidism, with bilirubin levels decreasing from 244 to 16 mumol/L (14.35 to 0.94 mg/dL). Deterioration in liver function in a patient with primary biliary cirrhosis as a result of hyperthyroidism has not previously been described.