Sputum cytology is useful for screening and diagnosis of centrally located lung cancer in Japan. On the other hand, cancer beyond the range of bronchoscopic visibility in X-ray negative patients can be detected only with difficulty. Of 265 patients detected by sputum cytology in mass screening, 85 had an abnormal chest roentgenogram and the remaining 180 were roentgenographically occult. A total of 200 roentgenographically occult squamous cell carcinoma lesions were detected in the above 180 patients. A total of 45 of the 200 lesions were bronchoscopically occult. Twenty-two of the above 45 lesions were beyond the range of bronchoscopic visibility with a standard bronchoscope. The data obtained show that a sputum cytology positive, X-ray negative squamous cell carcinoma may lie outside the reach of a flexible bronchoscope. Thus, when it is difficult to localize a cancer, brushing of the peripheral bronchi beyond bronchoscopic visibility and chest computed tomography should be performed.