A 67-year-old female was admitted to our hospital because of pneumonia-like shadow on chest roentgenogram with persistent cough and sputum of 4 months duration. Diagnosis as lung cancer was delayed more than 4 months. She showed fever and inflammatory reactions. Antibiotics were effective to inflammatory reactions, but not effective to pneumonia-like shadow. Transbronchial lung biopsy was useful for the diagnosis. Right lower lobectomy was performed. In this case, tumor extents were limited within one lobe. Tumor cells did not invade blood and lymphatic vessels, and extrathoracic metastases were not detected. The prognosis of bronchiolo-alveolar cell carcinoma was determined by intra-pulmonary tumor extent. Based on a comparison with the outcome of unresected cases, bronchiolo-alveolar cell carcinoma limited within one lobe should be surgically resected.