In order to explain a threefold increase in the incidence of meningococcal disease in the Netherlands during the 1980s, we serotyped and subtyped Neisseria meningitidis isolates recovered between 1958 and 1990 from > 3,000 patients with systemic disease. No single strain could be held responsible for the increase. Apart from the newly introduced strain B:4:P1.4, which became the most prevalent phenotype in 1990 (21% of all isolates), the majority of the cases in 1990 were caused by many different strains that were already present in the Netherlands before 1980. For the period 1980-1990, a shift in the age distribution of patients with meningococcal disease from younger to older age categories was found, particularly with regard to cases due to meningococci of serogroup B; this shift is explained by the changing distribution of serotypes and subtypes within serogroup B. A polyvalent group B, class 1 outer-membrane-protein vaccine of a stable composition could theoretically have prevented approximately 80% of all group B meningococcal infections in the Netherlands during the past 30 years.