Chromosome 1 abnormalities (C1As) are common genetic aberrations among patients with multiple myeloma (MM). We aimed to evaluate the significance of C1As among a contemporary cohort of patients with MM in the United States. We used electronic health records from the Flatiron Health database to select patients newly diagnosed with MM from January 2011 to March 2018 who were tested using fluorescence in situ hybridization within 90 days of diagnosis. We characterized patients as having documented C1As or other high-risk chromosomal abnormalities (HRCAs) as defined by the Revised-International Staging System (R-ISS) such as del(17p), t(14;16), and t(4;14). We used Kaplan-Meier methods to compare overall survival (OS) of patients with or without C1As and stratified log-rank tests (with the presence of HRCAs as a stratifying variable). We used Cox proportional hazards regression models to compare OS, adjusting for age, sex, stage, HRCAs, and type of first-line therapy. Of 3578 eligible patients, 844 (24%) had documented C1As. Compared with patients without C1As, patients with C1As were more likely to have higher stage (R-ISS stage III; 18% vs 12%), to have HRCAs (27% vs 14%), and to receive combinations of proteasome inhibitors and immunomodulatory agents (41% vs 34%). Median OS was lower for patients with C1As (46.6 vs 70.1 months; log-rank P,.001). C1As were independently associated with worse OS (adjusted hazard ratio, 1.42; 95% confidence interval, 1.19-2.69; P,.001), as were older age, higher R-ISS stage, HRCAs, and immunoglobulin A isotype. C1As were associated with inferior OS, independent of other HRCAs, despite greater use of novel therapies. Clinical trials testing newer therapies for high-risk MM should incorporate patients with C1As.