The determination of adenosine deaminase (ADA) is useful in countries where the prevalence of tuberculosis (TB) is high/ moderate. The objective of this study was to analyze the cut-off point for ADA in patients with TB at our institution. All patients with pleural effusion were included, from May 2016 to March 2019, except those with positive serology for HIV and transudates. They were grouped into the following diagnoses: TB, neoplasm, parapneumonic or other with an unclear cause. ADA determination and culture for mycobacteria were performed on all samples of pleural fluid. A ROC curve was performed to establish the best ADA cut-off point for the diagnosis of TB. Information was collected from 309 patients; 220 were included and 87 had a diagnosis of TB. The best cut-off point obtained for ADA was 52 U/l, with a sensitivity of 79% and a specificity of 90%. The area under the curve (AUC) was 0.90. In patients under 40 years old the best cut-off point was 41 U/l, below that obtained for the total study population. In our population the cut-off point for the ADA value in pleural exudate for the diagnosis of tuberculosis of 52 U/l presents the highest specificity and sensitivity.