Pleural lavage cytology (PLC) is the microscopic study of cells obtained from saline instilled into and retrieved from the chest during surgery for NSCLC. PLC is not reflected in the 7th TNM classification of lung cancer by the Union for International Cancer Control (UICC), although it is known that PLC-positive means worth prognosis. The reason is that information regarding the treatment of PLC-positive patients is still limited. On the other hand, malignant effusion is categorized M1a, and reflect the grade of malignancy more. The aim of this study is to evaluate the possibility of being an established independent predictor of prognosis and the efficacy of intrapleural chemotherapy (IPC) in PLC-positive patients. 1,165 of the 1,473 lung cancer patients who underwent surgery had undergone PLC before thoracotomy, following by a complete resection (PLC-positive:41 patients) and 16 patients with malignant effusion were evaluated. The treatment was performed for 16 patients with malignant effusion and 27 patents with PLC-positive. After pulmonary resection, IPC was performed after surgery, and the pleural cavity was filled with cisplatin with a normal saline solution. The disease-free survival (DFS) and the overall survival (OS) of the patients were evaluated. The pathological diagnosis showed that 41 patients (2.8 %) were positive for (or suspected to have) malignancy in their PLC. The univariate analysis showed that only T category and Lymph node metastasis were significant predictors of a PLC-positive status. The 5-year overall survival in PLC-positive patients was 37 % and that in PLC-negative patients was 75 %. The univariate (p<0.01) analyses showed that the status of PLC was significantly associated with the overall survival. Correction for differences in survival were obtained in the earlier stages than stage IIIA. Twenty-six of the 42 PLC-positive patients underwent IPC. The median survival time of the IPC group was 47.0months and that of those without IPC was 17.4 months (p<0.01), respectively. But, there are no significant differences between these groups with respect of DFS and recurrent site. PLC should be considered in all patients with NSCLC suitable for resection. A positive result can be an independent predictor of adverse survival especially in early stages. IPC may improve the OS in PLC-positive NSCLC patients and patients with malignant effusion, and a further prospective evaluation regarding this therapy is warranted.