Multiple myeloma may on rare occasions involve the breast. We report a case where a predominantly echo-poor solid mass was present on breast ultrasound in a patient under treatment for multiple myeloma. There was evidence of neovascularization on colour Doppler allowing a provisional diagnosis of carcinoma to be made. Fine needle aspiration cytology, however, demonstrated numerous mononuclear cells characteristic of myeloma. The appearances on ultrasound of this lesion have not been previously described.