During the period January 1980 to December 1990 (11 years) a retrospective study of patients with bacterial meningitis who were admitted to Bangkok Children's Hospital was carried out. There were 618 patients with 77 cases (12.5%) occurring below the age of one month (neonatal meningitis), and 541 cases (87.5%) between one month to 15 years (childhood meningitis). Pseudomonas aeruginosa was the most common pathogenic organism (16.9%) in neonatal meningitis; other causative agents in this age group included Klebsiella pneumoniae (13.0%), group B Streptococcus (11.7%), Escherichia coli and Enterobacter sp (10.4% each). In childhood meningitis, Haemophilus influenzae was the most common causative organism (42.3%), and followed by Streptococcus pneumoniae (22.2%) and Salmonella sp (12.4%). Excluding a 13 year-old leukemic patient, Salmonella meningitis occurred exclusively in infants, 87% of them were under six months, and 13% of them developed relapsing meningitis. Presenting symptoms and signs on admission of neonatal meningitis such as fever (81.8%), convulsions (45.4%), neck stiffness (22.5%), bulging fontanelle (33.3%) and Brudzinski sign (11.5%) were significantly less frequent than in the patients beyond the neonatal period (p < 0.05). The overall fatalities during 1980-1990 were 45.4% and 17.3% for neonatal meningitis and childhood meningitis, respectively. The fatalities of the two age groups declined significantly during 1987-1990 to 26.3% and 11.4% respectively.