A 56-year-old man in whom reticulonodular shadows had been noted on a previous chest radiography study was admitted to our hospital with complaint of exertional dyspnea in March 2004. His thoracic computed tomography (CT) showed diffuse ground-glass opacities and multiple centrilobular small nodules in both lung fields. Lymphocytes occupied a high proportion in the cells recovered from the bronchoalveolar lavage fluid. These findings were compatible with those for hypersensitivity pneumonitis. Histopathological findings observed in the video-assisted thoracoscopic surgical biopsy specimens included necrotizing granulomas, organizing pneumonia associated with collective epithelioid cell granulomas without necrosis, and alveolar septal thickening with lymphocyte infiltration that showed a centrilobular distribution. These findings were also compatible with those for hot tub lung. Further information that supported the diagnosis were the identifications of Mycobacterium avium complex in his sputum by acid-fast bacteriological culture as well as positive for Mycobacterium avium polymerase chain reaction in lung specimen. He responded well to corticosteroid therapy, resulting in improvement in his clinical condition as well as in his chest radiographs. He was later put on an antituberculosis therapy, and the corticosteroid therapy was discontinued. This led to an exacerbation of his disease and corticosteroid therapy was restarted. It is not long time since the disease was first recognized, and thus few cases have been reported in Japan. Our report may provide valuable information on the disease in this country.