From 1977 to 1981, 18,642 cases of bacterial meningitis were reported to the Centers for Disease Control. We analyzed data from 27 states with full participation from 1978 through 1981. Hemophilus influenzae was the most frequent cause of bacterial meningitis (48.3%), followed by Neisseria meningitidis (19.6%) and Streptococcus pneumoniae (13.3%). Overall attack rates for males were greater than for females (3.3 v 2.6 cases per 10(5) population per year). Attack rates were highest in children under 1 year of age (76.7 per 10(5) population per year). Case-fatality ratios were highest for gram-negative and miscellaneous causes of bacterial meningitis (33.7%) and lowest for meningitis caused by H influenzae (6.0%). Neisseria meningitidis and S pneumonia meningitis occurred preponderantly during the winter, while H influenzae meningitis had peak activity in the spring and fall. Ampicillin resistance among H influenzae increased from 18.7% in 1978, to 23.9% in 1981. Serogroup B Neisseria meningitidis was the most common serogroup identified during the reporting period (51.1%), followed by serogroup C (22.3%), serogroup Y (5.8%), and serogroup A (4.7%) infections.