The vaccination program instituted in Costa Rica in 1967 has had a great impact on measles. Since 1973 the downturn in its incidence and in mortality due to the disease are due solely to the continued vaccination of susceptible children throughout the country. An epidemic outbreak occurred in 1977. Since the vaccine was given primarily to children of school age, this outbreak probably was the result of an accumulation of susceptible subjects. There was little change in the mortality rates. Programs resulting in a coverage of 70% attempted to prevent a new outbreak in 1979, but failed. Because the vaccine was routinely administered to children one year of age and older, most of the cases were in the group younger than that age. At present, the incidence of measles is minimal, and no fatalities occurred in 1981. Vaccination coverage for children two years of age exceeds 90%, and Costa Rica's goal is the complete eradication of the disease.