A 65-year-old woman being treated under the diagnosis of pneumonia was subjected to further evaluation for right back tenderness. Chest radiography revealed a granular, net-like shadow in the right lower lung field, and right pleural thickening with pleural fluid retention. Ultrasonography demonstrated a cystic mass of uniformly low echo density, corresponding to the site of tenderness. This lesion was located on the right renal dorsal, right iliopsoas muscle ventral side. Based on CT findings of internal water density and marginal enhancement, the lesion was diagnosed as an abscess. With the suspicion of right tuberculous pyothorax with retroperitoneal gravitation abscess, puncture was attempted. The diagnosis was confirmed by the presence of Mycobacterium tuberculosis in the specimen. Antituberculosis chemotherapy was initiated, with drainage for symptom relief and lesion range definition. The abscess cavity communicated with the right pleural cavity via s stalk. The stalk path was confirmed by CT, and surgical curettage was performed. Tuberculous pyothorax with retroperitoneal gravitation abscess is rare and is not discussed in standard textbooks. In large series of cases it is not mentioned. In this patient we assumed that retroperitoneal gravitation abscess occurred as a result of the advanced state of tuberculous pyothorax.