BACKGROUND Gelatinous pleural effusion, due to raised hyaluronic acid, can be associated with pleural infection and malignancies, such as tuberculosis, metastatic pleural disease, and mesothelioma. This report is of an 80-year-old man presenting with a gelatinous pleural effusion and diagnosis of pleural mesothelioma. CASE REPORT An 80-year-old man with diabetes mellitus, ischemic heart disease, metastatic prostate cancer, 30-pack-year smoking history, and 5-year history of asbestos exposure (during his 30s), presented with a 4-week history of breathlessness and was found to have right-sided pleural effusion. Thoracic computed tomography (CT) showed mild right-sided pleural thickening. Pleural tap revealed exudative fluid, with a pH of 7.4, and unremarkable cytology and microbiology analyses. The patient was treated for pneumonia and para-pneumonic effusion and discharged home. He came back 5 weeks later with worsening of symptoms and re-accumulation of pleural fluid. Repeated thorax CT showed extensive right-sided pleural lobular thickening. Pleural tap again yielded an exudative fluid, with a pH of 7.37. Cytology and microbiology did not reveal any positive signs for malignancy or infection. This time the pleural fluid appeared gelatinous in consistency. Pleural biopsy showed atypical epithelioid mesothelial cells arranged in trabeculae, with a tubulo-papillary configuration. Also, immunohistochemistry panel showed tumor cells expressed calretinin, EMA, WT1, and D2-40, with negative TTF1, CEA, and BerEp4. Final diagnosis was epithelioid mesothelioma. CONCLUSIONS This report has shown that a gelatinous pleural effusion can be associated with malignant and inflammatory pleural diseases. In this case, imaging and pleural biopsy with histopathology confirmed a diagnosis of pleural mesothelioma.