Background: Pleural effusion (PE) is often classified as either a transudative or an exudative process. The aim of the study was to examine the causes of pleural effusions and the short- and long-term survival in the older patients hospitalized in the acute geriatric and internal medicine wards. Methods: Patients aged ≥ 65 years, who underwent thoracentesis, were included in this retrospective study. To distinguish between exudate and transudate PE, the Light’s criteria were applied. We compared medical indices and mortality in patients with exudate PE to those with transudate effusion according two age groups (65 - 85 vs. > 85 years). Results: The rates of the main etiologies of PE were congestive heart failure (CHF), 46%, lung infections, 25%, and malignancy, 12%, of the whole study population. Lung infections accounted for 53% of the exudate PE patients, with a higher presence among the >85 group of patients. The etiology of transudate PE was primarily CHF, more common among the patients of the >85 group. In malignancy, CHF and lung infections patients, the chances of dying within one year were 80.3%, 63.2%, and 45.5%, respectively. In transudate PE patients, ten-year survival of the 65-85 group of patients was significantly higher. In the exudate PE patients, there was no difference in survival between the two age groups. Right-sided and bilateral pleural effusions were associated with worse prognosis. Conclusion: Clinicians encountering patients with PE should be aware of their heightened mortality risks, and should carefully monitor their underlying etiology and employ appropriate optimal management.