CASE PRESENTATION: 70-year-old, immunocompetent, African American female with history of chronic dyspnea and hypoxia presented with worsening dyspnea and cough. She had recurrent hospital admissions in the preceding months with similar presentation, which were managed as COPD exacerbations. PFT results revealed restrictive pattern and no obstruction. Chest CT and HRCT both showed diffuse, interstitial pattern with fibrosis and traction bronchiectasis predominantly in upper lobes. Borderline enlargement of mediastinal lymph nodes were noted. Bronchoscopy, BAL, trans-bronchial biopsy and endobronchial ultrasound guided trans-bronchial needle aspiration were negative for sarcoidosis. BAL demonstrated predominantly macrophages without evidence of infection. An open lung biopsy showed patchy chronic inflammation with few eosinophils, multiple foci of atypical adenomatous hyperplasia with non-necrotizing granulomas in interstitium and airspace suggestive of hypersensitivity pneumonitis (HP). The granulomas were larger and well-formed than those typically seen in HP and resembled a pathologic picture seen in hot tub lung disease. HP panel for allergens were negative. On inquiring for exposure, patient reported use hot pool therapy twice (for joint pains), for 12 weeks, around the time of onset of dyspnea exacerbations. She also had exposure to hot pool 30 years ago. However, BAL specimen and lung biopsy were negative for AFB.