A 2-year-old girl presented with prolonged fever and progressive dyspnea for 3 weeks. A chest radiograph revealed a left lung infiltrate and associated pleural effusion. Echocardiography revealed a large posterior mediastinal mass extending to the left atrial wall and massive pericardial effusion. The presumptive diagnosis was lymphoma. At operation, a large brownish-yellow mass was noted at the posterior mediastinum, with matted hilar, and subcarinal lymph nodes. Pericardial and pleural effusions with left lung consolidation were also noted. Histopathological examination of biopsy specimens revealed a granulomatous inflammatory reaction with a diffuse eosinophilic infiltrate and broad septated fungal hyphae with right angle branching compatible with zygomycosis. Surgical removal of the mass could not be performed due to the adjacent great vessels and carina. She subsequently died from airway obstruction and respiratory failure ten days later.