This paper reviews 105 patients with breast cancer who had a pleural effusion as a direct consequence of metastatic disease. The mean lag time between diagnosis of primary tumor and presentation of the effusion was 41.5 months. Mean survival time after development of an effusion was 15.7 months. Of the 99 patients with unilateral breast tumors, 50% had ipsilateral effusions, 40% were contralateral, and 10% were bilateral. Forty-two percent of the patients had pleural effusion as the first evidence of recurrence. No particular group of women, based on age, menopausal status, or parity could be identified as being at risk of developing a subsequent effusion. However, there was a significantly higher proportion of patients who had central and medial tumors and who had Stage III cancers. Other tumor features, such as size, histologic type, or grade, did not predict the development of pleural metastasis. The success rate of a variety of treatment methods, local, general, or a combination of both, was 17% in achieving control of effusions. There may be a place for more aggressive treatment of pleural effusion at first presentation so that the quality of life could be improved during the patient's remaining months of survival.