The results of intraoperative cytodiagnosis by fine needle aspiration of 51 cases with lung masses are presented. The diagnosis of benign lesion in 17/51 cases and malignancy in 34/51 cases was established by cytology. The accuracy of this cytopathologic diagnosis was 100% in our series. In 34 cases with malignant lung tumors, the accuracy, as compared with histological diagnosis in cell type, was 84.2%. At thoracotomy, this approach is easy, safe and rapid and without any complication for undetermined pulmonary lesions. In some cases with a deep lesion, this approach has proved to be most useful to avoid a blind major pulmonary resection. We believe that intraoperative cytodiagnosis of lung masses by fine needle aspiration is a valuable supplementary diagnostic measure for pulmonary neoplasms.