In a prospective study of 111 cases of lung cancer, cytopathologic diagnoses were compared with histologic diagnoses. In 77.5% of the cases, histopathologic diagnoses were in concurrence with cytopathologic diagnoses. The discrepancies occurred mainly in poorly differentiated adeno and epidermoid carcinoma. Well differentiated adeno and epidermoid carcinoma were cell typed with 100% accuracy and small cell carcinoma with 90% accuracy.