Background: Pleural effusions are common in critically ill patients. However, the management of pleural fluid on relevant clinical outcomes is poorly studied. We evaluated the impact of pleural effusion in the intensive care unit (ICU). Methods: A large observational ICU database Multiparameter Intelligent Monitoring in Intensive Care III was utilized. Analyses used matched patients with the same admission diagnosis, age, gender, and disease severity. Results: Of 50 765, 3897 (7.7%) of critically ill adult patients had pleural effusions. Compared to patients without effusion, patients with effusion had higher in-hospital (38.7% vs 31.3%, P < .0001), 1-month (43.1% vs 36.1%, P < .0001), 6-month (63.6% vs 55.7%, P < .0001), and 1-year mortality (73.8% vs 66.1%, P < .0001), as well as increased length of hospital stay (17.6 vs 12.7 days, P < .0001), ICU stay (7.3 vs 5.1 days, P < .0001), need for mechanical ventilation (63.1% vs 55.7%, P < .0001), and duration of mechanical ventilation (8.7 vs 6.3 days, P < .0001). A total of 1503 patients (38.6%) underwent pleural fluid drainage. Patients in the drainage group had higher in-hospital (43.9% vs 35.4%, P = .0002), 1-month (47.7% vs 39.7%, P = .0005), 6-month (67.1% vs 61.8%, P = .0161), and 1-year mortality (77.1% vs 72.1%, P = .0147), as well as increased lengths of hospital stay (22.1 vs 16.0 days, P < .0001), ICU stay (9.2d vs 6.4 days, P < .0001), and duration of mechanical ventilation (11.7 vs 7.1 days, P < .0001). Conclusions: The presence of a pleural effusion was associated with increased mortality in critically ill patients regardless of disease severity. Drainage of pleural effusion was associated with worse outcomes in a large, heterogeneous cohort of ICU patients.