This study was done to analyze the epidemiology of invasive Haemophilus influenzae disease in Bochum city area. Forty-eight children with invasive Haemophilus influenzae infections were treated at the University Children's Hospital in Bochum during the study period from January 1971 to June 1992. Clinical manifestations included meningitis (n = 34), epiglottitis (n = 8), pneumonia (n = 2), bacteremia (n = 2), cellulitis (n = 1) and osteomyelitis (n = 1). The overall yearly incidence rate for all invasive Haemophilus influenzae infections was 13 per 100,000 children younger than five years of age, with a marked increase in the last six years. Haemophilus influenzae meningitis showed no significant change during the study period with an overall yearly incidence of 9 per 100,000 children younger than five years. Twenty-eight cases (58%) of all invasive Haemophilus influenzae infections occurred in patients under two years of age and five cases (10%) were younger than six months. Invasive Haemophilus influenzae disease showed no seasonal prevalence. All isolates were susceptible to ampicillin. No deaths occurred, but severe bilateral deafness resulted in one patient with meningitis. Prospective epidemiologic studies are needed to estimate clinical efficacy of the Haemophilus influenzae type b immunization program in Germany.