Malignant pleural effusions are most commonly associated with lung cancers, however, it also can be resulted from breast cancers, ovarian cancers, stomach cancers and so on. According to the their histologic types, adenocarcinoma have been known as the most common cell type of malignant pleural effusions and squamous cell carcinoma is rare. We herein present incidences, clinical characteristics and survivals of malignant pleural effusions according to their cell types and primary diseases. The objects are 84 malignant pleural effusion patients diagnosed by pleural fluid cytologic examination or pleural biopsy from Jan. 1992 to May. 1997 in Seoul National University Hospital. A retrospective chart review on their histologic types, biochemical parameters and survivals is described. Among 84 patients, 52 were males and the other 32 were females with 1.6 : 1 of male and female ratio and their mean age was 57.6 years old. Common symptoms of them were dyspnea, cough, sputum and pleuritic chest pain. The proportions of bloody nature of effusion, lymphocyte dominant pleural effusion, exudative effusions were 66%, 39% and 93%, respectively. They consisted of 54 cases of adenocarcinoma(33 cases of them were lung cancers), and 10 cases of squamous cell carcinoma (8 cases of them were lung cancers), 10 cases of malignant lymphoma, 8 cases of small cell lung cancer and a case of mesothelioma and leukemia. There was no differences in characteristics of effusions, clinical features and survivals between each histologic cell types. Analyzing them according to primary diseases, no difference except longer survivals in malignant pleural effusions from breast cancer than from other cancers was observed. In conclusion, considering the incidences of histologic types of lung cancers during same period (squamous cell carcinoma ; 47%, adenocarcinoma; 33%, small cell lung cancer; 12% and large cell carcinoma ; 2%), malignant pleural effusions more likely occurred in adenocarcinoma than other cell types of lung cancers and there was no significant difference of clinical characteristics between histologic types.