The epidemiology of hepatitis A, a disease endemic in various countries, is in a state of continuous change. Adults are more exposed to infection and considering the frequent absence of immunity, in contrast to children in whom the disease is almost always asymptomatic, the disease is often serious and prolonged with a mortality of up to 2.5%. The mode of transmission of HAV is predominantly the fecal-oral route; the virus is isolated during the prodromic period of the disease from the feces, blood, bile and seminal fluid. The virus can also be found in saliva (OMS '95); in addition it may also be transmitted by the maternal-fetal route. The HAV infects cells in vitro but does not cause a direct cytopathic effect. At the beginning of the acute phase of the disease the production of anti-HAV antibodies is of the IgM type followed later by IgG. Some studies have shown a potential role of cellular immunity in clearance of the virus from the hepatocytes and in the pathogenesis of the infection of HAV. The efficacy of immunoglobulin serum in the prevention of hepatitis A has been demonstrated since 1944. As regards active immunity two types of vaccinations have been prepared. One with live attenuated HAV carried by either bacteria or virus. The other, killed inactivated HAV, HAV capsule, antigenic subunit, synthetic peptides, anti-idiotypes or virosomes. The recent literature describe the vaccine produced by Merck Sharp & Dohme and by Smith Kline Beecham (SKB); both vaccines are made from HAV, grown in vitro, inactivated with formalin and adsorbed to aluminum hydroxide. The protection of the vaccine begins 14 days after administration and lasts from one month to one year. Numerous studies have been conducted which have shown that the vaccine is effective when given in 2 doses and confers protection against HAV for at least one year. The results have shown that the vaccination causes seroconversion in approximately 100% of subjects, and does not cause serious side effects and the acceptance of the vaccination worldwide has been good.