Hemophilus influenzae is a frequent cause of acute, purulent meningitis in children but is only occasionally responsible for meningeal infections in adults. A survey of the literature in English reveals only 44 cases of influenzal meningitis in patients over the age of 20 years.1-30 The present series of 11 additional cases has been compiled in order to review the clinical manifestations of this infection and to examine the circumstances associated with its appearance in the adult population. Report of Cases The patients described in this report were observed at the Grady Memorial Hospital, Atlanta; The Johns Hopkins Hospital, Baltimore; or The New York Hospital, New York, during the period from 1947 to 1959. The clinical and laboratory observations on these cases are summarized in the Table. The incidence of H. influenzae meningitis in adults with bacterial meningitis at these institutions was estimated to be at least 1%. Six of