Multiple myeloma is a rare cancer characterized by a proliferation of malignant plasma cells. Although the tumor cells remain primarily within the bone marrow, they can cause a number of complications, including localized bone destruction, anemia, decreased immunity to infection, and kidney damage. Multiple myeloma is more commonly diagnosed in persons over 65 years of age, in men than in women, and in blacks than in whites. Early diagnosis is difficult because symptoms may not appear until the cancer is advanced. The average 5-year survival rate is about 30%. Despite recent therapeutic advances that have improved the quality of life and length of survival, multiple myeloma is incurable at present. In addition to drugs that inhibit the destruction of bone, conventional treatment for multiple myeloma involves chemotherapy and corticosteroids. Bone marrow transplantation also may be beneficial. Newer treatment approaches include immunomodulating therapies and targeted agents. Ongoing research in the field aims to elucidate the etiology of multiple myeloma and develop more effective treatments.