Cases of acute bacterial (excluding tuberculous) meningitis and meningococcal infection, occurring in children under 10 years of age in the North-West Metropolitan region between 1969 and 1973 have been studied retrospectively by case-note review. The risk of having an acute meningococcal infection was estimated to be 1 in 1090, and that of having an attack of haemophilus meningitis to be 1 in 1500, but the age of 10 years. The case-fatality rates for meningococcal infection, haemophilus meningitis, and pneumococcal meningitis were 10.9%, 5.7%, and 16.4% respectively. Meningitis was not diagnosed in life in 26 of 94 fatal cases (28%).