Children less than one year old behave as the group with the highest incidence of meningococcal disease during all the epidemic period in the past '80s decade in Cuba. There were used chronological series of monthly incidence rates between 1983 and 1990, in order to identify the behavior of seasonality, taking into account the clinical form and the insert of years 1989 and 1990 in the series: in both of them a massive antimeningococcal vaccination campaign took place. It is evident that seasonality has a different behavior in accordance with the clinical form: it is like the countries from the northern hemisphere with a moderate climate for the meningoencephalitis, and like the countries of the southern hemisphere with a warm climate for the meningococcal syndrome. Months of the rainy period have the lowest seasonal index. Modifications of these seasonal patterns are not found after executing the vaccination.