A 48-year-old man was admitted because of persistent dry cough for six months. He had been a smoker for 25 years, averaging a pack a day, and demonstrated clubbing of the fingers. Basilar fine crackles were observed in both lung fields. Chest X-ray films on admission showed diffuse reticulonodular shadows. Chest computed tomograms showed low-attenuation areas mainly in the center of the upper lung field, and ground-glass opacity, air bronchiolograms, and perivascular interstitial thickening of the peripheral vessels mostly in the lower field. A Gascintigram disclosed mild accumulation in both lungs. A transbronchial lung biopsy specimen did not reveal special features. However, a biopsy specimen obtained by thoracoscopy showed evidence of respiratory bronchiolitis, with a mononuclear inflammatory process involving respiratory bronchioles and adjacent air space, associated with mild fibrous thickening of the peribronchiolar interstitium and surrounding alveoli septa. These findings suggested that the patient had respiratory bronchiolitis-associated interstitial lung disease, the second case to be reported in Japan.