Four members of a Chinese family who had thyrotoxicosis and periodic paralysis are described. Two of these patients had "hashitoxicosis' (Graves' disease and Hashimoto's thyroiditis) as evidenced by the presence of thyroid antibodies in addition to elevated thyroxine (T4) levels. The other two patients were not available for testing. The association of the familial occurrence of "hashitoxicosis' and periodic paralysis does not appear to have been reported previously.