The diagnosis of active myeloma requires 10% or more plasma cells on bone marrow examination (or biopsy proven plasmacytoma), M protein in the serum and/or urine (except in patients with true nonsecretory myeloma), and evidence of end-organ damage (hypercalcemia, renal insufficiency, anemia, or bone lesions) secondary to the underlying plasma cell disorder. Multiple myeloma accounts for approximately 10% of hematologic malignancies. Almost all patients are thought to evolve from an asymptomatic premalignant stage termed monoclonal gammopathy of undetermined significance (MGUS). MGUS is present in over 3% of the population above the age of 50 years and progresses to myeloma or related malignancy at a rate of 1% per year. In some patients, an intermediate asymptomatic but more advanced premalignant stage referred to as smoldering multiple myeloma can be recognized clinically.