Complete response (CR) is considered an important goal in most hematologic malignancies. However, in multiple myeloma (MM), there is no consensus regarding whether immunofixation (IF)-negative CR, IF-positive near-CR (nCR), and partial response (PR) are associated with different survivals. We evaluated the prognostic influence on event-free survival (EFS) and overall survival (OS) of these responses pre- and post-transplantation in newly diagnosed patients with MM. We analyzed 632 patients from the prospective Grupo Español de Mieloma 2000 protocol who were uniformly treated with vincristine, carmustine, cyclophosphamide, melphalan, and predisone/vincristine, carmustine, adryamcine, and dexamethasone induction followed by high-dose therapy and autologous stem-cell transplantation. Post-transplantation response markedly influenced outcomes. Patients achieving CR had significantly longer EFS (median, 61 v 40 months; P < 10(-5)) and OS (medians not reached; P = .01) versus patients achieving nCR, who likewise had somewhat better outcomes compared with patients achieving PR (median EFS, 34 months, P = .07 v nCR; median OS, 61 months, P = .04). EFS and OS and influence of response were similar among older (age 65 to 70 years) and younger (age < 65 years) patients. Similar findings were observed with pretransplantation response, with trends toward EFS (P = .1; P = .05) and OS (P = .1; P = .07) benefit in patients achieving CR versus nCR and PR, respectively. Post-transplantation response was markedly influenced by pretransplantation response; improvements in response were associated with prolonged survival. Quality of response post-transplantation, notably CR, is significantly associated with EFS and OS prolongation in newly diagnosed patients with MM. There were trends toward similar associations with pretransplantation response status.