Patients undergoing autologous stem cell transplantation (ASCT) for multiple myeloma (MM) undergo disease assessment approximately 100 days later. Some patients continue to have a decline in their serum or urine monoclonal protein after day 100 in the absence of additional therapy. We evaluated 430 MM patients who underwent ASCT within 12 months of their diagnosis and had not achieved a complete remission at day 100. Of these patients, 167 (39%) had a continued response after day 100 without additional therapy. When compared with patients who did not (n = 263), those who had a continued response had a longer progression-free survival (35 vs 13 months, P < .001), time to next therapy (43 vs 16 months, P < .001), and overall survival (96 vs 57 months, P < .001). This phenomenon of a continued response maintained prognostic value in a multivariable analysis and should be considered when interpreting posttransplant responses.