Achieving a complete response (CR) is associated with improved overall survival (OS) in multiple myeloma (MM), but data on duration of CR (DurCR) are limited. We evaluated 351 patients (2004-2016), achieving CR with first-line therapy. Patients with sustained DurCR ≥ 24 months (n = 177) had better OS; 150 vs. 81 months, p < 0.001. DurCR ≥ 24 months remained a significant predictor for OS (HR: 0.3, 95% CI: 0.2-0.5, p < 0.001) after adjusting for age, revised ISS stage, transplant and maintenance therapy. Landmark analysis at 24 months demonstrated similar results, OS: 150 vs. 83 months, p < 0.001. Survival benefit persisted even after loss of CR, with median OS being 89 vs. 56 months (p = 0.005), respectively. Patterns of loss of CR were heterogeneous, with biochemical relapse in 59 (25%); symptomatic relapse in 58 (24%); positive immunofixation/monoclonal protein rise not meeting relapse/progression criteria in 88 (37%) and abnormal free light chain ratio in LC MM in 34 (14%) patients. OS from start of first-line therapy was superior in patients starting second-line treatment for biochemical vs. symptomatic relapse (125 vs. 81 months, p = 0.001). This is likely attributable to underlying disease biology and prevention of end-organ damage by early treatment initiation, as benefit was independent of R-ISS stage.