In order to decide whether vaccination for measles, mumps and rubella should be introduced at the age of five years, calculations of the immunities in various age groups were performed until the year 2002 with and without vaccination at the age of five years. These calculations are based on the knowledge of immunity in the various age groups before the MMR vaccination programme was instituted in 1987 and knowledge of the compliance with vaccination obtained to date. Future predictions reveal that it is of decisive significance that compliance with vaccination among 12-year-olds is increased as rapidly as possible to 0.7 and to 0.8 in the subsequent year, if the level of immunity present prior to institution of the vaccination programme is to be maintained. The second vaccination given at a shorter interval after the first would prevent about 150 cases of illness in all per annum among 6-12 years-old. However, this should not be introduced at the expense of vaccination at the age of 12 years, which should be continued for at least 10-15 years yet. Possible abandoning of vaccination at the age of 12 years 10-15 years hence presupposes that adequate numbers of the children have been vaccinated twice at an early age and that it is sufficiently certain that secondary failure of vaccination does not occur to any significant extent.