INTRODUCTION : To study cerebrospinal fluid (CSF) adenosine deaminase (ADA) activity in meningitis cases for diagnosis and differential diagnosis of Tuberculous meningitis. Material and Method: The study was conducted in 100 cases & divided in different patient groups by relevant investigations. CSF ADA estimation was done by spectrophotometry. Result: Statistically significant higher values of CSF ADA were observed with TBM compared to pyogenic meningitis and aseptic meningitis (p<0.001). The sensitivity and specificity was 96% and 100% respectively when a cut off value of ADA 9 IU / L was used. The PPV , NPV, and accuracy of ADA test in diagnosing TBM was 100%, 96.15% and 98% respectively. Conclusion : Our study concluded that CSF ADA level can be used as simple , rapid and inexpensive test for diagnosis of TBM.