• We studied the epidemiology of reported Hemophilus influenzae meningitis in Colorado for the years 1977 through 1981. Of 340 culture-confirmed cases, 94% occurred in children less than 5 years old. A marked seasonal variation was present, with peaks in late fall—early winter and late spring. The percentage of H influenzae isolates resistant to ampicillin increased from 4.2% in 1977 to 31.3% in 1981. The incidence of reported disease in children younger than 5 years of age increased from 26 per 100,000 population in 1977 to 39 per 100,000 population in 1981. The overall case fatality rate was 5.2%; mortality was somewhat higher for persons with ampicillin-resistant infections (9.4%) than for those with ampicillin-sensitive infections (4.3%). Our results agree with previous reports of an increasing rate of ampicillin resistance in H influenzae meningitis and indicate a possible increasing incidence of this disease in Colorado.