Multiple myeloma (MM) is characterized by progressive proliferation of malignant plasma cells, usually initiating in the bone marrow. MM can affect any organ; a total of 7 - 18% of patients with MM demonstrate extramedullary involvement at diagnosis. Non-secretory multiple myeloma (NSMM) is a rare variant that accounts for 1 - 5% of all cases of multiple myeloma. The disease is characterized by the absence of monoclonal gammopathy in serum and urine electrophoresis. Our case report highlights the diagnostic challenge of a case of NSMM with extensive extramedullary involvement in a young female patient who initially presented with right shoulder pain and bilateral breasts lumps. Skeletal survey showed multiple lytic bony lesions. The initial diagnosis was primary breast carcinoma with osseous metastases. No monoclonal gammopathy was found in the serum or urine electrophoresis. Bone marrow and breast biopsies revealed marked plasmacytosis. The diagnosis was delayed for a month in view of the lack of clinical suspicion of multiple myeloma in a young patient and scant biochemical expression of non-secretory type of multiple myeloma.