BACKGROUND: The aim of this study was to clarify to what extent bacterial meningitis could be distinguished from aseptic or tuberculous meningitis through C-reactive protein (CRP) in adults. METHODS: We retrospectively analyzed the medical records of 91 patients aged 15~81 years who had been hospitalized for acute meningitis and underwent lumbar puncture due to suspected central nervous system infection. RESULTS: We included 50 patients with aseptic meningitis, 23 patients with acute bacterial meningitis, and 18 patients with tuberculous meningitis. Blood CRP was higher in bacterial meningitis. None of the patients with bacterial meningitis had a CRP value of under 20 mg/dl. The CRP values were under 20 mg/dl in 92% of the patients with aseptic meningitis and in 73% of those with tuberculous meningitis. Taking a CRP level of above 20 mg/dl as a positive discriminatory factor for bacterial meningitis, the sensitivity and specificity were 1.0, 0.88. To better predict whether a patient has bacterial or nonbacterial meningitis, we developed a canonical discriminant function equation using CRP and CSF parameter, and finally concluded that blood CRP was a good predictive indicator that differentiated bacterial meningitis from aseptic or tuberculous meningitis at admission. CONCLUSIONS: The CRP measurement, is easily performed and inexpensive. We believe it is worth analyzing CRP whenever meningitis is suspected, it can also limit the unnecessary use of antibiotics.