Hot-tub lung is a diffuse granulomatous interstitial lung disease that develops in immunocompetent individuals caused by inhalation of aerosolized nontuberculous mycobacteria (usually Mycobacterium avium complex), which can occur if a contaminated hot tub is used. It may represent hypersensitivity reaction, infection, or both. Diagnostic criteria include detection of nontuberculous mycobacteria in sputum, bronchoalveolar lavage, or lung biopsy specimen, usually by cultures.