Acute hepatitis E occur commonly as outbreaks in endemic areas, but can occur sporadically in other part of the world. Acute hepatitis E has been reported rarely in Korea. A case of concurrent acute hepatitis E virus (HEV) infection and hyperthyroidism was reported in an inactive hepatitis B surface antigen carrier. We experienced two cases of concomitant acute HEV infection in patients with hyperthyroidism. The first case had acute HEV infection with subclinical hyperthyroidism while taking propylthiouracil. The second case suffered from acute HEV infection in a patient with Graves' disease intractable to propylthiouracil. Herein, we suggest the possible association between HEV infection and hyperthyroidism.