Nocardiosis is an opportunistic infection occurring in immunocompromised patients. Worldwidely, about four cases of nocardiosis of the breast have been previously reported, but none of these were in Korea. We describe a case of breast nocardiosis associated with pulmonary infection in a patient with Cushing's disease. In our patient, multiple, well-defined, conglomerated, tubular-shaped, isodense mass was revealed at mammography, and an irregular-shaped, ill-defined, heterogeneous echoic mass with movable debris at ultrasonography.