A 59-year-old Japanese man with chronic HBV infection was admitted to our hospital with fever, cough, and bloody sputum in March 2007. HBV surface antigenemia had been confirmed when he was 29 years old. He had a history of sustained fever with multiple pulmonary consolidative shadows, which was diagnosed as cryptogenic organizing pneumonia on the basis of the clinical course, the laboratory and radiographic findings, and the results of bronchoscopic examination, including transbronchial lung biopsy, in December 2004. High-dose corticosteroid, including pulse methylprednisolone, had led to remission, and corticosteroid therapy was tapered off for 11 months without any relapse of the disease until August 2006, when he developed high fever without lung involvement. Prednisolone, 30 mg/d, which was empirically used after possible exclusion of infectious and malignant diseases, resolved his condition. In October 2006, when prednisolone was tapered to 5 mg/d, fever relapsed, with cough, bloody sputum, and lung nodules. Serologic studies, including Cryptococcus and Aspergillus antigens determined by enzyme-linked immunosorbent assay, and β-D-glucan, were negative. Bronchoscopic examination failed to yield the diagnosis. Corticosteroid was tapered off within 4 weeks, and antimicrobial agents, including IV ciprofloxacin and voriconazole, started from December 2006 were ineffective. From February 2007, his symptoms and the pulmonary lesions progressively deteriorated, and he was transferred to our hospital. On admission, he had a 7-kg weight loss, and his temperature was 39.1°C. He had received neither corticosteroids nor immunosuppressants for > 4 months before admission to our hospital. Otolaryngologic examination, and repeated urinalyses revealed no abnormalities. Echocardiogram showed no valvular abnormalities suggesting infectious endocarditis. Abdominal ultrasound showed that the liver had a mildly irregular surface and mildly coarse parenchymal texture, which were consistent with advanced chronic hepatitis, although splenomegaly was absent. No other organ involvement was observed. Leukocyte count was 9,600 /μL without eosinophilia. C-reactive protein was 9.62 mg/dL. The test for antinuclear antibodies, antineutrophil cytoplasmic antibodies (ANCA) by immunofluorescence assay; myeloperoxidase-ANCA, proteinase 3-ANCA, and antiglomerular basement membrane antibodies by enzyme-linked immunosorbent assay were all negative. Immune complex detected by C1q-binding assay was positive (7.3 μg/mL, normal range < 3.0), but cryoglobulins and hypocomplementemia were not observed. The HBV surface antigen was positive, but the HBV envelope antigen was negative with positive corresponding antibodies. The HBV-DNA level was 7.2 log10 copies/mL, and the HBV was type C and had both precore and core promoter mutations. Hepatitis C virus, human T-cell leukemia virus, and HIV virus serologies were negative. Repeated blood cultures were negative. CT scan-guided needle biopsies of the largest nodule in the right lung showed necrotic tissues, foci of neutrophils with nuclear dusts, and no granulomas. Ziehl-Neelsen and Grocott stains demonstrated neither acid-fast bacilli nor fungi. Bacterial cultures and polymerase chain reaction for TB-DNA using the biopsied tissues were negative. During the 5 weeks after admission, the febrile state continued and the pulmonary nodular and cavitary lesions deteriorated progressively, despite treatment with IV ampicillin/sulbactam, meropenem, vancomycin, minocycline, or oral sulfamethoxazole/trimethoprim (Fig 1). Surgical biopsy of the newly emerged lung nodule (Fig 1C) showed necrotizing vasculitis involving the small artery to arterioles of pulmonary arteries, organizing pneumonia, and neutrophilic bronchiolitis and microabscesses without granulomatous changes (Fig 2). Prednisolone, 60 mg/d, and entecavir, 1 mg/d, rapidly resolved his symptoms and normalized the C-reactive protein level within 1 week after the start of the treatment. Entecavir was maintained, and the HBV-DNA level has remained undetectable. To date, there has been no relapse of vasculitis while tapering the dose of corticosteroid without the use of immunosuppressants.