CASE INFORMATION: C.D. is a 44-year-old female with Grave's disease treated with propylthiouracil for two years. She presented with a 2 week history of productive cough, fevers, pleuritic chest pain and fatigue. She was diagnosed with right lower lobe pneumonia and admitted for IV antibiotics. Despite appropriate therapy, the patient's condition deteriorated and she developed hemoptysis and progressive hypoxemia that required intubation. CXR showed bilateral alveolar infiltrates. Bronchoscopy was consistent with diffuse alveolar hemorrhage. Admission CBC revealed pancytopenia. Her PTU was discontined. Additional labs included serum perinuclear antineutrophil cytoplasmic antibody (p-ANCA) > 160, proteinase 3 antibody 10 ( > 2 positive), myeloperoxidase antibody 8 ( > 6 positive), decreased C3 and C4, microscopic hematuria and negative ANA, anti-Smith, anti-RNP and HIV. The patient was diagnosed with p-ANCA vasculitis secondary to PTU and was treated with pulse dose steroids with stabilization of alveolar hemorrhage. She was extubated several days later. DISCUSSION: PTU is the most common antithyroid drug prescribed for Grave's disease.