The classification of squamous cell carcinomas, based on cellular differentiation features, includes the poorly differentiated epidermoid carcinomas and well-differentiated epidermoid carcinomas. The histogenetic cytologic data clarify conventional cytodiagnosis of poorly differentiated epidermoid carcinomas and poorly differentiated adenocarcinoma, and also eliminate other categories such as large cell carcinoma and small cell anaplastic carcinoma. We conducted a study for evaluating the degree of differentiation of pulmonary squamous cell carcinoma in 620 patients - 551 men (88.8%) and 69 women (11.1%) who had lung cancer confirmed by cytologic, histologic and bronchoscopic examination. The cytologic examination was performed on slides with samples obtained by bronchial brushing and prints of bronchial biopsy stained with the Giemsa method. Histopathologic examination was performed on samples obtained by bronchial biopsy and stained with Hematoxylin-Eosin. At cytologic examination we found: poorly differentiated epidermiod carcinomas in 66 cases (33.8%), moderately differentiated epidermoid carcinomas in 22 cases (11.2%) and well differentiated epidermoid carcinomas in 107 cases (54.8%). Histological examination revealed: poorly differentiated epidermoid carcinomas in 133 cases (45.7%), moderately differentiated epidermoid carcinomas in 32 cases (10.9%), and well differentiated epidermoid carcinomas in 126 cases (43.2%). Our results suggested the importance of the association between cytologic and histopatologic examinations in the diagnosis of lung cancer.