PURPOSE: Routine collection of patient-reported outcomes (PROs) for patients with advanced solid malignancies is an evidence-based practice and critical component of high-quality cancer care, but real-world adherence is poorly characterized. We sought to describe real-world adherence to PRO monitoring and its potential predictors. METHODS: We conducted a retrospective cross-sectional study using deidentified electronic health record data from a National Cancer Institute Cancer Center, encompassing one academic and two community sites. Participants included individuals with lung cancer receiving systemic therapy from January 1 to December 31, 2019. The primary outcome was patient-level adherence, defined as the proportion of treatment visits during which a PRO questionnaire (spanning symptoms, functional status, and global quality-of-life domains) was completed within 30 days. Practice-level performance was calculated as unadjusted mean patient-level adherence. We modeled patient-level adherence using multivariable ordinary least squares regression and identified covariates associated with adherence using a significance threshold of P < .05. RESULTS: In 2019, there were 18,604 encounters for 1,105 patients with lung cancer (mean [standard deviation] age 65.8 [10.2] years; 621 [56.2%] female; 216 [19.6%] Black) receiving systemic therapy. The mean patient-level PRO adherence ranged from 27.2% to 70.0% across sites and was 49.4% overall. Advanced age (≥ 65 years) and Black or African American race were negatively associated with PRO adherence ( P < .01). CONCLUSION: Across this real-world cohort of patients undergoing treatment for lung cancer, adherence to PRO monitoring lagged that achieved in seminal clinical trials, with potential age- and race-based disparities, demonstrating an implementation gap that could be addressed with standardized reporting of an adherence-based quality metric.