Cytogenetic studies were performed as part of all diagnostic and surveillance bone marrow examinations in 956 newly diagnosed patients with multiple myeloma (MM) receiving total therapy (TT) protocols and in 1085 previously treated patients enrolled in non-TT protocols. In both groups, cytogenetic abnormalities (CA) were present in one-third at baseline and persisted in 14% prior to first and 10% prior to second transplant (TT, 5%; non-TT, 15%); post-transplant detection rates increased progressively with time, from 7% within 6 months to 21% within 24 months to 28% at relapse. According to multivariate analyses, overall survival was adversely affected by the presence of CA at baseline (hazard ratio (HR)=7.20, P<0.001) and the development of CA both prior to (HR=3.28, P<0.001) and after first transplant (HR=6.24, P<0.001), whereas suppression of CA pretransplant was favorable (HR=0.38, P<0.001). The presence of CA at relapse further distinguished patients with a short median post-relapse survival of only 11 versus 47 months in those without CA (P<0.0001). Post-relapse survival was independently adversely affected by the detection of CA both at baseline (HR=1.35, P=0.044) and relapse (HR=2.47, P<0.001). Collectively, these results underscore the importance of monitoring for CA and attest to the favorable prognostic consequences of CA suppression with effective therapy.