To appreciate the present results, certain issues need to be discussed. First, our study partly includes a period in which bacterial meningitis caused by H influenzae type b was still present, although today it has almost been eradicated by vaccination.30 Modifying the group to exclude patients with H influenzae type b (n = 32), however, did not alter the results and yielded the same CSF and clinical scoring rule. Second, the CSF rule has been developed in a population of patients with meningeal signs as the main problem. This rule does not apply to all patients suspected of having meningitis, since patients with a prominence of other symptoms of meningitis (such as convulsions and coma) but without meningeal signs at presentation are not included in our study population.2,3,31 To our knowledge, however, this is the first study in a pediatric emergency department based on the patient's clinical presentation. Third, in some children the reference standard (lumbar puncture) for the outcome bacterial meningitis was missing (n = 18). In these children, absence of bacterial meningitis has been assessed using follow-up data. Although this could have introduced some diagnostic verification bias,32 we think this did not occur in our study, since bacterial meningitis is a serious and fatal disease without adequate treatment2 and all children without a lumbar puncture were followed up and recovered uneventfully. We may, however, have misdiagnosed some cases of viral or aseptic meningitis. Since we aimed to distinguish between the presence or absence of bacterial meningitis, this will not affect our results. Fourth, the aim of our rule was to define patients in whom empiric treatment for bacterial meningitis could be safely omitted. However, after bacterial meningitis has been ruled out, some of these children may require antibiotic treatment for other conditions, such as septicemia, urinary tract infections, or pneumonia, pending the results of further investigations. Fifth, our study was performed at a pediatric university hospital. Ninety percent of patients visiting the emergency department of this hospital, however, require basic pediatric care.17 Therefore, we think that the derived prediction rule is applicable both to academic and general hospitals. Finally, internal validation of the CSF model by bootstrapping demonstrated that the rule is robust. Before implementation of this decision rule in clinical practice, however, a prospective validation in similar future patients is necessary and currently being performed in our hospital. Subsequently, impact analysis is necessary to see how the rule really functions in practice and if a reduction of lumbar punctures and hospitalizations for empiric treatment will be achieved.