Aim of the work: To study cases of malignant pleural effusion in AL Kasr AL Aini Hospital.Methods: Pathology reports from malignant pleural effusion patients were obtained from the archives of the pathology department, cytology unit in Kasr AL Aini Hospital.Results: Non-mesothelioma (metastatic) cases are the most common cause of malignant pleural effusion.Recommendations: Use of immunohistochemical stains in differentiating adenocarcinoma from malignant mesothelioma.