BACKGROUND: Since delayed diagnosis and treatment of bacterial meningitis worsens patient prognosis, clinicians have a low threshold to perform a lumbar puncture or to start empiric antibiotic treatment in patients suspected of having meningitis. OBJECTIVE: To develop a decision rule, including cerebrospinal fluid (CSF) indices and clinical characteristics, to determine whether empiric antibiotic treatment should be started in children with meningeal signs. DESIGN: Multivariable logistic regression analysis of retrospectively collected data. Bacterial meningitis was defined as a CSF leukocyte count of more than 5/ micro L with positive bacterial culture findings from CSF or blood specimens. SETTING: Pediatric emergency department of a pediatric university hospital. PATIENTS: A total of 227 children (aged 1 month to 15 years) with meningeal signs. MAIN OUTCOME MEASURE: The diagnostic value of adding early obtainable CSF indices to clinical characteristics to predict bacterial meningitis. RESULTS: Independent predictors of bacterial meningitis from early obtainable CSF indices were the CSF polymorphonuclear leukocyte count and the CSF-blood glucose ratio. The diagnostic value (area under the receiver operating characteristic curve) of this CSF model was 0.93. Application of the model together with clinical characteristics could predict early the absence of bacterial meningitis in 69 (30%) of the 227 patients so that empiric antibiotic treatment could be safely withheld. CONCLUSION: A diagnostic decision rule that uses clinical characteristics at admission, the CSF polymorphonuclear leukocyte count, and the CSF-blood glucose ratio is a useful tool for deciding whether to start empiric antibiotics in children with meningeal signs.