We report a case of iliopsoas abscess caused by Aspergillus fumigatus with pulmonary complications. A 60-year-old man was admitted to the Showa University Hospital Department of Gastroenterology with fulminant hepatitis B on April 14, 2010, and treated with steroids. Although fulminant hepatitis B was improved by steroid and symptomatic therapy, he developed a fever on hospital day 39. The chest X-ray film showed a nodular lesion in the right middle-lower lung field, and both the (1 → 3)-β-D: -glucan and Candida mannan antigen tests were positive. The β-D: -glucan level increased despite treatment with fluconazole and other drugs, including low-dose micafungin. Abdominal computed tomography showed a low-density area in the right iliopsoas muscle. He was then referred to the Department of Clinical Infectious Diseases. A. fumigatus was isolated from the iliopsoas lesion and the pulmonary lesion after specimens were obtained by aspiration and bronchofiberscopy, respectively, leading to a diagnosis of fungal iliopsoas abscess. Steroid therapy was tapered early, the abscess was drained, and the micafungin dose was increased. This treatment led to improvement of the fever, inflammatory reaction, β-D: -glucan level, and lesions of the lung and iliopsoas muscle. In preparation for discharge, treatment was changed to voriconazole (parenteral → per oral) followed by itraconazole (per oral). His clinical course was satisfactory, and there was no recurrence after antifungal therapy was stopped. We conclude that after invasive pulmonary aspergillosis developed, A. fumigatus spread hematogenously to create an extremely rare iliopsoas abscess. The β-D: -glucan level closely reflected the response to treatment and was useful for follow-up.