This study evaluated the usefulness of Intraoperative imprint cytology for establishing the nature of lung tumours otherwise undiagnosed. From 1994 to 1995, 185 patients (127 men, 58 women) treated with surgery for lung tumours, were examined by imprint cytology of the resected tumour tissue at the time of thoracotomy. Cytologic smears were fixed with the use of spray fixative, then sent immediately for hematoxylin-eosin staining and microscopic evaluation. The results were compared with the histological findings from paraffin sections of the surgical specimens.Of the 185 patients, 88% were correctly diagnosed. There were 95 true positive results (51.3%), 68 true negative (36.8%), and 18 false negative (9,7%). Four results (2,2%) were false positive for malignancy on cytologic criteria. The sensitivity of the procedure was 84%, the specificity 94.4%, and the diagnostic accuracy 88.1%.Although cytologically the distinction between different types of lung cancer was sometimes difficult, the authors conclude that intraoperative imprint cytology can be used as a quick, non-invasive and low cost method of diagnosis.