Viral hepatitis is one of major causes of liver diseases in Korea. Acute hepatitis that is characterized by symptoms of fatigue, nausea, anorexia, malaise, and jaundice is caused by various hepatitis viruses such as hepatitis A, B, and C virus. Viral hepatitis has 4 clinical phases, incubation period, preicteric phase, icteric phase, and convalescence period. Hepatitis A is spread by the fecal-oral route, and is associated with poor sanitary conditions. Sometimes acute hepatitis A shows prolonged cholestatic hepatitis or recurrent hepatitis after a convalescence period; however, acute hepatitis A is usually self-imited and does not progress to chronic hepatitis. Hepatitis B virus can cause both acute and chronic hepatitis. Acute hepatitis B shows similar clinical manifestations as in hepatitis A, however, chronic hepatitis can develop in about 5% of acute hepatitis B. Chronic hepatitis B is the major cause of chronic liver diseases such as liver cirrhosis and hepatocellular carcinoma in Korea. The route of chronic infection correlates with vertical infection and sexual contact because hepatitis B virus is spread by the parenteral route. Recently hepatitis B vaccine can protect the transmission of hepatitis B virus effectively from mother to neonate, so the incidence of carrier state in child ages is very low. Hepatitis C virus can also cause both acute and chronic hepatitis. Acute hepatitis C shows similar clinical manifestations as in hepatitis A; however, chronic hepatitis can develop in about 80~90% of acute hepatitis C. Chronic hepatitis C is also one of the major causes of chronic liver diseases in Korea.