A 58-year-old healthy woman was admitted to our hospital on 8th October, 1991 for detailed investigation of an abnormal shadow on chest roentgenogram, which was detected by mass survey. The chest roentgenogram showed a cloudy shadow of the right upper lobe, and retrospectively, this abnormal shadow had been present since 1986. Flexible fiberoptic bronchoscopy showed complete obstruction of right B1b bronchus by regenerated bronchial mucosa. Aseptic pus was detected in the obstructed bronchus by means of transbronchial aspiration cytology (TBAC) and chronic lung abscess was diagnosed. The chest roentgenograms of this case is very unusual, and we were unable to find a similar case of chronic lung abscess diagnosed by means of TBAC.