Background and Study aim: Serum procalcitonin (PCT)  is  specific for the diagnosis of bacterial infection. The aim of this study is to evaluate the role of serum PCT in diagnosis of septic meningitis in adults and its efficacy in differential diagnosis. Patients and Methods: The study included 30 adults of septic meningitis and 30 adults with aseptic meningitis admitted in Menouf Fever Hospital and Tropical Medicine Department with fever, headache, vomiting and seizure. The diagnosis of septic meningitis was based on clinical features; physical examination, blood and cerebrospinal fluid (CSF) cytochemical findings, Gram stain and bacterial culture. Thirty cases of aseptic meningitis admitted during same period were also included in the study, and 20 subjects of matched age and sex, free from any CNS diseases undergoing spinal anaesthesia for non CNS surgical causes as control. Serum PCT was measured by Gloryscience ELISA Kit. Results: Serum PCT level was significantly higher in patients with septic meningitis than those with aseptic meningitis (P<0.001). In culture and Gram stain positive 23 and 20 cases respectively, serum PCT was significantly elevated (23.123 ± 9.894 pg) than aseptic meningitis (8.652± 1.777pg) (P<0.001). At optimum cut off value of ≥10.36 pg/mL, based on area under receiver operating characteristic (ROC) curve, PCT showed sensitivity, specificity of 100 % and 86.6% respectively for the differentiation of septic from aseptic meningitis. Conclusions: Serum PCT may be used as diagnostic marker for septic meningitis and its differentiation from aseptic meningitis.