A 74-year-old woman was incidentally found to have a left breast mass. The mass could not be adequately compressed to be visualized on mammography. Ultrasonography showed a heavily-calcified rounded mass in the left axillary tail of the left breast. Chest radiograph confirmed that the mass was a migrated humeral head. Remotely-displaced fracture-dislocations of the humeral head are very rare and to our knowledge, displacement into the breast, clinically mimicking a breast mass, has not been previously described.