The study describes the case of a 67-year-old woman initially diagnosed with a right-sided exudative pleural effusion thought to be tuberculous pleuritis; the effusion was predominantly mononuclear with elevated levels of adenosine deaminase (ADA) and lactate dehydrogenase (LDH), and cytology was negative. Contrast-enhanced CT showed right-sided pleural nodules and partial pleural thickening, prompting CT-guided percutaneous needle pleural biopsy and further investigations. A bone marrow biopsy and flow cytometry of the pleural fluid were also performed as part of the diagnostic process. The final diagnosis was B-lymphoblastic lymphoma confirmed histologically and by flow cytometry. After the administration of chemotherapy, the patient showed significant improvement and almost disappeared pleural effusion at the recent follow-up. The authors point out that malignant pleural effusion from lymphoma can easily be mistaken for tuberculous pleurisy with elevated ADA and LDH values. They recommend examination of pleural fluid by flow cytometry and active collection of histological samples; for extensive pleural thickening, they prefer CT-guided percutaneous pleural biopsy.