Introduction: Pleural effusion is common in medical ICU (MICU) patientsand may affect patient outcomes. Objective:This study aimed to determine the prevalence, causes, and clinical significance of pleural effusion in critically ill patients. Methods: A total of 500 patients included in the present study. The patients initially had pleural effusion or effusion developed during their ICU stay. Results: Overall, 350 patients were males and 150 were females, and their mean age was 51.5±18.6 years. Pleural effusion was found to be exudates in 60% of cases and transudates in 40%. Uncomplicated parapneumonic effusion was the most common cause (18%), followed by heart failure (16%). The cause of pleural effusion did not significantly affect the patient outcome or duration of ICU stay. No significant reduction in duration of ICU stays or ICU mortality was seen in patients who received therapeutic aspiration or tube drainage compared with patients who received no specific management for effusion.