To identify risk factors for the development of bacterial meningitis, we compared clinical characteristics in children with occult bacteremia who did and those who did not subsequently develop bacterial meningitis. The estimates of risk were adjusted for the possible confounding effects of other characteristics by using logistic regression. Of 310 children (median age 15 months) who had occult bacteremia with Streptococcus pneumoniae, Haemophilus influenzae type b, or Neisseria meningitidis at either Yale-New Haven Hospital or Children's Hospital of Pittsburgh, bacterial meningitis subsequently developed in 22 (7%). Compared with the risk associated with occult bacteremia with S. pneumoniae, the adjusted relative risk for bacterial meningitis was 85.6 (P less than 0.0001) and 12.0 (P = 0.0001) for N. meningitidis and H. influenzae type b, respectively. By contrast, the adjusted relative risk associated with a lumbar puncture at the initial visit was only 1.2 (P = 0.78). The development of bacterial meningitis in children with occult bacteremia is strongly associated with the species of bacteria that causes the infection, but not with a lumbar puncture or with other clinical characteristics identifiable at the initial visit.