The underlying plasma cell clones in multiple myeloma (MM) and Ig light-chain amyloidosis (AL) appear to be different not only in terms of 'tumor burden' but also in terms of their underlying biology. High-dose chemotherapy with auto-SCT is one method of reducing the clone size and thereby improving OS. Post-auto-SCT outcomes between the two diseases have never been formally compared. Among all patients with a diagnosis of AL or MM who received auto-SCT as primary therapy at the Mayo Clinic, Rochester, there were higher CR rates (40% versus 29%, P<0.0001) in the AL group. The respective median OS for the AL and MM patients was 113 and 59.5 months, respectively, P<0.0001. Among patients achieving CR, MM patients had a fivefold risk of death as compared with AL patients. Although auto-SCT cannot be offered to all patients with either AL or MM, it appears that for those well enough to be chosen for the procedure, greater benefit is derived among the AL patients. This difference in survival is most notable among those patients who achieve CR, suggesting very different plasma cell biology between the two diseases.