Quality of response is associated with prolonged overall survival (OS) in newly diagnosed multiple myeloma patients. This cohort study within the phase 3 Assessment of Proteasome Inhibition for Extending Remissions (APEX) trial of bortezomib versus dexamethasone in relapsed myeloma assessed the relationship between quality of response to bortezomib (n = 315) and clinical benefit. Treatment-free interval (TFI), time to alternative therapy (TTAT), time to progression (TTP) and OS were assessed in response-evaluable patients in the bortezomib arm in cohorts defined by achievement of complete response (CR; n = 27), very good partial response (VGPR; n = 31), partial response (PR; n = 77), minimal response (MR; n = 21) or non-response (NR, including stable and progressive disease; n = 159). CR was associated with significantly longer median TFI (24.1 vs. 6.9/6.4 months) and TTAT (27.1 vs. 13.6/14 months) versus VGPR/PR. Median TTP was similar in CR, VGPR and PR cohorts; median OS was not reached. Patients achieving MR appeared to have prolonged median TFI (3.8 vs. 2.3 months), TTAT (8.7 vs. 6.2 months), TTP (4.9 vs. 2.8 months) and OS (24.9 vs. 18.7 months) versus NR. In conclusion, bortezomib had substantial activity in relapsed myeloma patients; CR may be a surrogate marker for significant clinical benefit with bortezomib. MR appeared to be valid as a separate response category in this setting.