Study objective: To assess the reliability of meningeal signs and other physical findings in predicting bacterial and aseptic meningitis at various ages. Design: Children requiring lumbar puncture were evaluated prospectively for meningeal signs and other physical parameters before lumbar puncture. Setting: Emergency department of Children's Hospital of Wisconsin. Participants: One hundred seventy-two children, aged 1 week to 17 years, with meningitis (53 bacterial and 119 aseptic). Measurements and main results: Nuchal rigidity was present in 27% of infants aged 0 to 6 months with bacterial meningitis versus 95% of patients 19 months or older (P = .0001). Three percent of infants 0 to 6 months old with aseptic meningitis had nuchal rigidity versus 79% of patients 19 months or older (P = .0005). Seventy-two percent of infants 12 months of age or younger with bacterial meningitis had at least one positive meningeal sign versus 17% of infants with aseptic meningitis (P = .0001). Eighty-five percent of children older than 12 months with meningitis had at least one positive meningeal sign, 93% with bacterial meningitis, and 82% with aseptic meningitis. Conclusion: Despite a lack of meningeal signs, a high index of suspicion for meningitis is essential when evaluating the febrile infant 12 months of age or younger. © 1992 Miles Inc. Pharmaceutical Division.