Clinical manifestations of hypothyroidism are very various and these degree are related to the severity and duration of the disease. Pericardial effusions, one of the manifestations of hypothy- roidism, were relatively common in the past. However, recently they may not be so frequent representative of hypothyroid subjects. The higher frequency of Hashimotos thyroiditis in Turners syndrome, especially those with an X-isochromosome, compared with the general population is well known. The pathophysiological process of autoimmunity is thought to be linked with the presence of an abnormal X-chromosome. Recently we experienced a case of X-isochromosome Turners syndrome with hypothyroidism and pericardial effusion and report it with reviews of the literatures. (J Korean Soc Endocrinol 12:661-666, 1997)