Clinical discharge and laboratory records were reviewed in the seven government hospitals that provide care for 93% of the pediatric population of Santiago, Chile, to detect cases of meningitis and other invasive (bacteremia-associated) infections caused by Haemophilus influenzae. infections that occurred in children less than five years of age from January, 1985, through December, 1987, were recorded and matched with census data to calculate incidence rates. The incidence of meningitis and non-meningitis syndromes peaked in the 6- to 11-month age group and tapered sharply after 12 months of age. The city-wide incidence (ca. 21.6 cases/10(5) children less than 5 years of age) is one-third to one-half that reported for the general pediatric population in the United States. However, there is much evidence for under-reporting in Santiago. In Area Norte, served by Roberto del Rio Children's Hospital where H. influenzae has been a subject of research by pediatricians for years, the incidence of invasive H. influenzae infections (42.5/105) is approximately two-fold higher than the rest of Santiago. The cumulative proportions of episodes of H. influenzae disease occurring in successively older age groups closely parallel the pattern seen in the general United States pediatric population. Although only ca. 20% of all episodes occur during the first 6 months of life, nearly 80% of episodes are seen by 18 months of age. Based on the observed incidence rates, the apparent underreporting and the high city-wide case fatality of Hib meningitis (16%), invasive H. influenzae infections represent an important public health problem in Santiago, Chile.