Data from a large phase III trial (Myeloma XI) were examined to determine the relationship between MRD status, PFS, and OS in post-ASCT patients randomly assigned to lenalidomide maintenance or no maintenance at 3 months after ASCT. At ASCT + 3 and ASCT + 9, MRD-negative status was associated with improved PFS and OS. Sustained MRD negativity from ASCT + 3 to ASCT + 9 or the conversion to MRD negativity by ASCT + 9 was associated with the longest PFS/OS.