Hepatitis E caused by hepatitis E virus (HEV) is a serious public health concern in developing countries where HEV is mainly transmitted through contaminated water. Recently, in industrialized countries, autochthonous hepatitis E, a porcine zoonosis, has been increasingly recognized. In Japan, the number of national notifications of acute hepatitis E has increased since the introduction of anti-HEV IgA antibody measurement, covered by the national health insurance program, in 2011. In the past three years, we examined five patients of acute hepatitis or acute-on-chronic liver failure caused by HEV infection who presented various clinical courses in the southern area of Ibaraki prefecture in Japan. Of these patients, 78-year-old and 63-year-old male patients presented acute hepatitis E and recovered by only bed rest. The latter patient had a history of consuming grilled or undercooked pork and shellfish prior to the onset of hepatitis E. Among the five patients examined, the infection route was detected only in this patient. Of note, a 65-year-old female patient presented severe hepatitis associated with painless thyroiditis. The patient was diagnosed with probable autoimmune hepatitis and was successfully treated with prednisolone (40 mg/day). Lastly, 58-year-old and 62-year-old male patients, both of whom had a history of diabetes mellitus and alcoholic liver disease, developed acute-on-chronic liver failure, and the latter patient with pre-existing liver cirrhosis died due to liver failure. Thus, patients with clinical HEV infection who display multiple underlying diseases can develop acute-on-chronic liver failure. In conclusion, HEV infection manifests the diverse clinical courses.