Haemophilus meningitis was found to be rare in those more than 6 years of age in The Netherlands (incidence: 1/10(6)/year). Persons of this age account for only 6-7% of all cases. The histories of a representative sample of 35 of 73 patients over the age of 6 years with Haemophilus influenzae meningitis were reviewed and correlated with the characteristics of the causal strains. Altogether, these patients had suffered 51 episodes of purulent meningitis. Sequelae were found after five of the 35 H. influenzae episodes studied (14%) but none of the patients died during one of these episodes. Of all the patients, 54% had severe predisposing factors, mainly CSF leaks following road traffic accidents or operations, which often led to recurrent bouts of meningitis; these patients were predominantly males. In the patients aged 15-64 years, predisposing factors were present in 74%. Predisposed patients were infected mainly by unencapsulated strains and, as far as type b strains were involved, by uncommon subtypes. Unencapsulated strains were hardly ever able to invade the bloodstream, primarily or secondarily. Careful review of the patient's history is important in this rare disease, because, in many patients, the presence of a CSF fistula may become evident and surgery is likely to prevent recurrences.