question: Diffuse alveolar hemorrhage (DAH) is a life-threatening condition associated with various systemic diseases. Evaluation includes determining an underlying etiology. Isolated pauci-immune pulmonary capillaritis (IPIPC) without clinical, serological, or histological evidence of an underlying systemic process is an extremely rare cause of DAH. In limited case series, treatment is similar to treatment of DAH secondary to vasculitis or autoimmune disease and consists of immunosuppression. Prognosis is generally favorable. We present a case of a healthy male with IPIPC who, despite treatment, had persistent and ultimately fatal DAH. A 64-year-old male presented with mild dyspnea and scant hemoptysis. Review of systems was unremarkable. There was no history of travel or exposures. Hemoglobin was 12.0 g/dL, creatinine was 0.9 mg/dL, and urinalysis was normal. CT scan of the chest showed bilateral patchy ground glass opacities. Nasal swab for SARS-CoV-2 was negative. Bronchoscopy confirmed diffuse alveolar hemorrhage. He was started on methylprednisolone 1g daily for 3 days, followed by 1 mg/kg daily. Coagulation studies, ANA, RF, ANCA, and anti-GBM antibodies were negative. ESR was normal, but CRP was elevated at 29 mg/L. His echocardiogram was normal. Six days after bronchoscopy, he underwent a surgical lung biopsy. Pathology showed mostly bland alveolar hemorrhage with scattered areas of neutrophilic infiltration of the alveolar walls. Immunostaining was negative. Cyclophosphamide 2 mg/kg was initiated on day 14. The patient was maintained on nasal oxygen but had persistent slow alveolar bleeding. On day 22, plasmapheresis was initiated. Despite after 5 treatments of plasmapheresis, bleeding persisted. Cyclophosphamide was discontinued and rituximab was initiated. Over the next four weeks, bleeding accelerated with worsening hypoxemia, which ultimately led to intubation. The patient spent two weeks on the ventilator with need for daily blood transfusions. Gas exchange worsened with progressive hypoxemia and hypercapnia. Nine weeks after his initial presentation, the patient expired after family requested for palliative extubation. Autopsy showed hemorrhagic lungs without evidence of infection or malignancy. Isolated pauci-immune pulmonary capillaritis is rare. Since it was first described in 1995, there have been a limited number of cases described in literature. Current treatment recommendations are similar to treatment of DAH due to vasculitis, which include corticosteroids combined with cyclophosphamide or rituximab. Prognosis is generally favorable. Progressive and relentless hemorrhage as described in this case is unusual.