Minimal residual disease (MRD) is a concept that has gained significant value as a prognostic predictor and has become an emerging constituent of complete response (CR) reassessment in multiple myeloma (MM) patients. Studies in MM have demonstrated that up to 30% of patients achieving a CR after high-dose therapy will still have detectable MRD in the bone marrow as measured by standard-sensitivity flow cytometry or by molecular assays. Virtually every study examining MRD in MM has reported that among patients achieving a CR, those who were MRD negative (MRD-) had a significantly superior progression-free survival, with some studies reporting superior overall survival.