Tuberculous meningitis is the most severe form of tuberculosis. Because of high morbidity and mortality rates, early diagnosis and treatment are very important. For diagnosis of tuberculous meningitis there is requirement for rapid laboratory tests with high sensitivity. For this purpose, in this study the contribution of cerebrospinal fluid (CSF) Adenosine Deaminase (ADA) activity measurement to the diagnosis of tuberculous meningitis was evaluated. Twenty suspected tuberculous meningitis cases and 20 control cases were taken into the study. Cerebrospinal fluid ADA measurements were 16.02 + 10.95 U/L and 2.30 + 1.27 U/L in these two groups, respectively. In the suspected tuberculous meningitis group CSF ADA activity was significantly higher than the control group (p= 0.000). Specifity and sensitivity of the CSF ADA levels were calculated for different cut-off values. As conclusion, measurement of CSF ADA activity was found to be helpful in the diagnosis of tuberculous meningitis.