TYPE: Late Breaking Abstract TOPIC: Occupational and Environmental Lung Diseases INTRODUCTION: Hypersensitivity pneumonitis (HP) is caused by an inhaled agent. Usual cytopathologic findings include peri-bronchial and alveolar lymphocytic inflammation, poorly formed granulomas, and scattered areas of organizing pneumonia. Alveolar hemorrhage is a rare presentation. CASE PRESENTATION: 63 y/o male with history of asthma and multiple hospital visits due to respiratory distress, presented with shortness of breath and hypoxemia for 2 weeks. Physical exam, showed O2Sat: 85% (RA), tachypnea, and bilateral wheezes. Chest CT Angiography showed no evidence of pulmonary embolism but demonstrated bilateral patchy peribronchovascular groundglass consolidation in a mosaic attenuation, centrilobular nodules and focal areas of airspace consolidation. Laboratories remarkable for leukocytosis with eosinophilia and elevated procalcitonin. He was admitted with diagnosis of Pneumonia and treated with antibiotics without improvement. Bronchoalveolar lavage showed granulomatous inflammation and iron stain strongly positive in numerous alveolar macrophages. All cultures were negative. Further investigation revealed that he had multiple birds inside the house. Systemic steroids were started with rapid improvement of clinical presentation. Upon removal of the birds from home, he has not further exacerbations for the next 6 months. A diagnosis of non-fibrotic HP secondary to bird exposure was done. DISCUSSION: HP can be misdiagnosed as a viral illnesses, pneumonia, or asthma. Poor response to pneumonia treatment can be a clue during exacerbations, although the use of steroids for conditions as asthma can mask the condition. Also, atypical pathologic presentations as alveolar hemorrhage can occur. CONCLUSIONS: The diagnosis of HP requires a high index of suspicion and careful attention to exposure history, and possible atypical histopathologic findings. DISCLOSURE: No significant relationships. KEYWORD: Hypersensitivity Pneumonitis