Objective:Patients with cerebrospinal fluid (CSF) pleocytosis are routinely admitted to the hospital and treated with parenteral antibiotics, although few have bacterial meningitis (BM). The aim of this study was to evaluate predictors to dif-ferentiate BM from aseptic meningitis (ASM). Methods:The study was conducted in Razi hospital, a training center affiliated to Ahvaz Joundishapoor University of Medical Sciences in Iran. And all patients were 18 years old or above and were treated in the hospital between 2003 and 2007. Data of those who had meningitis, tested as CSF pleocytosis but had not received antibiotic treatment before lumbar puncture were retrospectively analyzed. Results: Among 312 patients with CSF pleocytosis, two hundred fifteen (68.9%) had BM and ninety seven (31.1%) had ASM. The mean age for patients with BM was (34.7±17.7) years (P=0.22, NS). Sixty percent of the BM cases and 61.2% of the ASM cases occurred in men (P=0.70, NS). We identified the following predictors of BM:CSF-WBC count > 100 per micro liter, CSF-glucose level < 40 mg/dL, CSF-protein level > 80 mg/dL. Sensitivity, specificity, PPV, NPV of these predictors, and LR for BM are 86.5% ,52.6% ,80.2%, 63.7% and 104. 1 for CSF-WBC count and 72.1%, 83.5%, 90.6% ,57.4% and 164.2% for CSF glucose, and 49.7%, 91.8%, 93.4% ,45. 2% and 104.5% for CSF protein. Conclusion:The CSF WBC count should not be used alone to rule out bacterial meningitis. When it is combined with other factors such as CSF glucose and protein improved decision making in patients with suspected BM may occur.