Malignant pleural effusions (MPEs) are a common complication of advanced malignancies, particularly lung and breast cancer. They are caused by a variety of mechanisms including tumor obstruction of lymphatic flow, spread of malignant cells via the systemic circulation, and tumor invasion of the pulmonary arterioles. Therapy is determined by tumor histology, stage of malignancy, and a careful assessment of a patient's performance status and comorbid diseases. A number of approaches have been used to treat patients with MPE ranging from thoracentesis to pleurectomy. Tube thoracostomy drainage followed by application of a sclerosing agent is the most common strategy. Effective sclerosing agents include quinacrine, talc, bleomycin, tetracycline and Corynebacterium parvum. Results from a recent multicenter randomized trial suggest that bleomycin may be superior in terms of control of effusion at 30 days. Further randomized studies are ongoing to determine the optimal method of draining the pleural space and the most effective sclerosing agent. Thoracoscopy using video-assisted techniques is a promising new approach to MPEs both for diagnosis and treatment. The application of biological agents such as interleukin-2, the interferons, and novel chemotherapeutic agents are experimental approaches that are under investigation.