We conducted a 3-year Taiwan-wide hospital-based survey of invasive Haemophilus influenzae infections in children less than 15 years of age. From January 1992 to December 1994, 105 cases (57 boys, 48 girls) were reported. Seventy-three patients (69.5%) had meningitis and 32 patients had other diseases (12 pneumonia, 10 sepsis, 7 cellulitis, 3 arthritis). Fourteen patients (13%) died, all of whom had meningitis or sepsis. Among the 63 patients who survived meningitis, 17 (27%) had neurologic sequelae and eight (47%) had hearing impairment. The number of cases of H. influenzae meningitis (30%) and other H. influenzae diseases (29%) peaked in children between 6 and 12 months of age. Patients with invasive infections (82%) and meningitis (73%) were younger than 24 months of age. Only 12 patients (11%) were older than 5 years of age and four had underlying diseases. The annual incidence of invasive H. influenzae infections in children less than 5 years old was 1.9 per 100,000 per year. During the same period a survey of purulent meningitis in children younger than 15 years of age was also conducted in 20 hospitals. A total of 198 patients, in whom the causative organisms were identified, were included; 94 patients were 2 months of age or under and the most frequent pathogen was group B streptococci (35 cases, 37%). Among the 104 patients who were older than 2 months of age, H. influenzae was the leading cause (38 cases, 37%). In conclusion, invasive H. influenzae type b (Hib) diseases exist in Taiwan but have an incidence lower than in Western countries. Hib meningitis is still the most common cause of purulent meningitis in children in Taiwan and is an important cause of mortality and morbidity. Continuous active surveillance of invasive H. influenzae infections is suggested to determine the best time to introduce an Hib conjugate vaccine in Taiwan.