SummaryStreptococcus pneumoniaeis one of the most frequent causes of pneumonia, meningitis, and otitis media. Persons at high risk are young children, elderly, and individuals with immunodeficiency or with an underlying disease. Thanks to a network ot 111 laboratories spread all over Belgium, the evolution of the number of deep isolates ofS. pneumoniaehas been followed from 1986 to 1991: the recorded frequency increased with a mean number of isolations per laboratory and per year rising from 3.6 in 1986to6.2in 1991.The objectives of this paper are to study the evolution of age and sex distribution of the patients, and of the origin of the isolates, and to propose solutions for slowing down this evolution.