Background: Autochthonous hepatitis E occurs sporadically in developed countries. The consumption of undercooked pork containing hepatitis E virus genotype 3(HEV-3) or 4(HEV-4) is the major risk factor for infection. The serological diagnostic kits currently used in hospitals sometimes produce false-negative or-positive results. Therefore, detection of both HEV RNA and antibodies to the virus is required for confirmative diagnosis of hepatitis E. Objectives: We aimed to detect HEV in serum samples from patients with cryptogenic hepatitis and to determine the origin of HEV. Study design: A nested polymerase chain reaction (PCR) method was developed for detection of HEV-3 and HEV-4 in patients with hepatitis. A total of 23 serum samples, deposited in 2006-2012, from patients with acute cryptogenic hepatitis who were serologically negative for hepatitis A, B, C, and E were examined using this method. The amplified PCR products were genetically analyzed. Results: Four HEV-4 isolates were detected from the 23 serum samples. Phylogenetic analysis indicated that three of the four isolates were closely related to HEV-4 isolates found in pigs in Korea and in patients with hepatitis E in Japan. Conclusions: The newly developed nested PCR method was useful for detection of HEV in patients with cryptogenic hepatitis. The close relationship between the human HEV-4 isolates identified in this study and swine isolates implied that zoonotic transmission of HEV might be a source of infection in patients with hepatitis. (C) 2017 Elsevier B.V. All rights reserved.