Case 1: A 57-year-old man presented with cough that had persisted for 2 months. Chest computed tomography (CT) revealed multiple small centrilobular nodules and reticular shadows. Bronchoalveolar lavage fluid (BALF) showed lymphocytosis and Mycobacterium avium complex (MAC) in mycobacterial culture. Transbronchial lung biopsy (TBLB) revealed bronchiolocentric alveolitis, fibrosis, and granulomas. Case 2: An 83-year-old woman, who was case 1’s mother and lived with him. She had been undergoing treatment for MAC for 3 years; however, her CT examination revealed worsening of interstitial pneumonia. Her BALF and TBLB showed results similar to case 1. MAC was detected from the bathtub at their home that is automatically self-cleaned by bubbles; therefore, both cases were diagnosed as familial hot tub lung. Cases of familial hot tub lung are rare; hence, we report the cases here with the course of treatment.