The age incidence of meningococcal infections occurring between 1984 and 1991 in England and Wales was determined from data submitted with isolates to the Meningococcal Reference Laboratory for England and Wales. The incidence was maximum at 6 months of age and thereafter declined sharply to the age of 4 years. It was followed by a small secondary peak at 17-18 years. There was a relative excess of group B infections in the early months of life and, although group B and group C infections both peaked at 6 months of age, the latter did not decline until after the age of 9 months. Certain strains of meningococci were more likely to be associated with disease in older children and young adults.