Surveillance data on measles in Yaoundé during the 8 years from 1968-1975 have been reviewed. Measles epidemics occurred in every year except 1969-1970, the period of the attach phase of the Smallpox Eradication and Measles Control Programme. Subsequent biennial mass measles immunisation campaigns and maintenance measles immunisation at the child health centre failed to interrupt epidemic transmission. 70-80% of cases were under 24 months of age. Annual outbreaks occurred during the first half of each year, but smaller numbers of cases continued throughout the year. The outbreaks came to an end despite 32-41% of 6 through 36 month old children remaining susceptible. The seasonality of measles was not simply related to the annual rainfall pattern. Rather it is hypothesised that measles seasonality depends on the movement of young children with their mothers during the annual agricultural cycles. Measles immunisation programmes must be adapted to local epidemiological and cultural conditions in order to interrupt transmission.