Pulmonary disease due to Mycobacterium avium complex (MAC) typically occurs in patients with impaired cellular immunity or chronic lung disease. Recently, there has been an increase in the number of reports of pulmonary disease caused by MAC occurring in otherwise healthy individuals, including those reporting recent hot tub use. It is not clear if this respiratory illness represents a true infectious process or a hypersensitivity pneumonitis. We report a case of diffuse pulmonary disease caused by MAC in an immunocompetent individual after hot tub use. The patient's clinical course, transbronchial lung biopsy results, and microbiologic examination findings all pointed to a hypersensitivity reaction due to MAC. With avoidance of the hot tub, and no pharmacological treatment, the patient had complete resolution within 2 months. In light of the number of new cases of "hot tub lung" in otherwise healthy individuals, clinicians should advise their patients of the potential risk associated with hot tub use.