BACKGROUND Pleural effusion is a common complication of many disease processes. Disorders causing distortion in body fluid mechanics will cause either transudative effusions or exudative effusions. Lights criteria are used to differentiate Exudative from Transudative Effusions. The present study is undertaken to study the aetiology and clinical features of pleural effusion in our institute. Tuberculosis is still one of the most important causes of exudative plural effusion. The levels of Adenosine De Aminase an enzyme found in most cases are increased and its determination has proven to be useful as diagnostic test in case of TPE. Elevated plural fluid ADA predicts TB plural effusion with a sensitivity of 90-100% and specificity of 89-100%. METHODS 100 cases of pleural effusion admitted in Katuri Medical College were carefully studied, and investigated. Skiagram postero-anterior view of chest with both domes of diaphragm were done for all patients. Ultrasound chest-for estimating the quantity of fluid and site of aspiration was done in all cases and sent for pleural fluid ADA, counts, protein, sugar and LDH values. Pleural fluid cytology for malignant cells and gun biopsy of the malignant mass was done in 2 cases. Immunohistochemistry was done in both malignancies for TTF-1 and p40 for confirmation of squamous and adeno carcinomas respectively. RESULTS 100 cases of pleural effusion were studied in a 2-year period in the Department of Pulmonology, Katuri Medical College, Chinakondrupadu. Among 100 cases, 97 are exudates and 3 cases are transudates. Tuberculosis is the most common cause of exudative pleural effusion (91 cases). CONCLUSIONS Out of 100 cases of pleural effusion 97 cases were exudates and 3 were transudates. Tuberculosis was the most common cause of exudative pleural effusion. Malignancy was the second most common cause. Congestive cardiac failure was the most common cause of transudative pleural effusions. The estimation of pleural fluid differential counts was important for ruling out other causes. ADA is a reliable tool for diagnosis of tuberculosis when applied along with Light's criteria.