Hepatitis A virus (HAV) is a small, non-enveloped RNA virus belonging to the Picornaviridae, for which only one serotype has been identified. Transmission is usually through the faecal-oral route by person-to-person contact. The most common risk factors are household or sexual contact with a sufferer, attendance or working at a day-care centre, international travel, and association with food or waterborne outbreaks; 55% of cases have no identifiable risk factors. HAV infection may be symptomatic or asymptomatic, and shows three phases. Virus is shed during the incubation phase, anti-HAV IgM appears during the symptomatic phase and can be used for diagnosis, and anti-HAV IgG appears at the same time but persists lifelong. Unusual clinical manifestations of hepatitis A include cholestatic, relapsing and fulminant hepatitis. Hepatitis A accounts for 93% of cases of acute hepatitis in Argentina, including 7% of atypical clinical cases. Hepatitis A is the major cause of fulminant hepatitis, and has been reported to account for 10% of liver transplants in children in France and 20% in Argentina. One-year survival after liver transplantation is 64%. Prevention must be considered as the main means of averting this severe illness.