Objectives: Measures of health-related quality of life (HRQOL) are collected throughout healthcare systems and used in clinical, economic, and outcomes studies to direct patient-centered care and inform health policy. Studies have demonstrated increases in stressors unique to the COVID-19 pandemic, however, their effect on HRQOL is unknown. Our study aimed to assess the change in self-reported global health during the pandemic for patients receiving care in a large healthcare system compared with 1 year earlier.Methods: An observational cross-sectional study of 2 periods was conducted including adult patients who had a healthcare appointment and completed the Patient-Reported Outcomes Measurement Information System Global Health (PROMIS GH) as standard care during the COVID-19 pandemic and a year earlier. The effect of time on PROMIS global mental health (GMH) and global physical health (GPH) was evaluated through multiple statistical methods.Results: There were 38 037 patients (mean age 56.1 ± 16.6 years; 61% female; 87% white) who completed the PROMIS GH during the pandemic (August 2020) and 33 080 (age 56.7 ± 16.5 years; 61% female; 86% white) who had completed it 1 year earlier (August 2019). GMH was significantly worse, whereas GPH was similar during the pandemic compared with a year earlier (adjusted estimate [standard error]: -1.21 (0.08) and 0.11 (0.08) T-score points, respectively).Conclusions: Our study found modest, nonclinically meaningful decreases in GMH and similar GPH during the COVID-19 pandemic compared with a year earlier in patients cared for in a large healthcare system. Nevertheless, healthcare systems are likely seeing a biased sample of patients during these times. Findings from our study have implications for the interpretation of HRQOL during this pandemic. [ABSTRACT FROM AUTHOR]