Hot tub lung is a lung disorder associated with exposure to hot tub water contaminated with Mycobacterium avium complex (MAC). Although its pathogenesis remains unclear, it may be considered hypersensitivity pneumonitis (HP) rather than an infectious disease. We report a case which fulfilled the current diagnostic criteria of hot tub lung. A patient had worked as a cleaner in the public bath for approximately one year and presented with dyspnea for over one month. The computed tomographic finding of bilateral ground glass attenuation and pathologic finding of granulomatous inflammation were consistent with HP. MAC was isolated from bronchoalveolar lavage fluid and hot tub water. After corticosteroid treatment without antimycobacterial medication, the patient improved and there has been no recurrence. The patient has since discontinued working in the public bath.