We report a case of Mycobacterium avium complex (MAC) infection showing a solitary pulmonary mass. High-resolution computed tomography (CT) revealed a well-defined, lobulated mass (32x25 mm) without calcification, cavitation, or bronchiectasis on the right upper lobe. There were no abnormalities in other sites of the lung even on high-resolution CT. The diagnosis was established by open lung needle biopsy. The patient exhibited a large solitary pulmonary mass caused by MAC infection, suggesting that, although the incidence is rare, MAC infection can show a solitary mass that is radiographically indistinguishable from lung cancer.