Context: Systematic collection of patient-reported outcomes (PROs) reduces symptom burden and improves quality of life. The ability of older adults to complete PROs, however, has not been thoroughly studied. Objectives: To determine whether older adults with advanced cancer received assistance completing PROs, the nature of the assistance, the factors associated with receiving assistance, and how the prevalence of assistance changed over time. Methods: Data were obtained from a multisite cluster randomized controlled study of geriatric assessment (Clinicaltrials.gov: NCT02107443). Adults ≥70 years with advanced cancer completed multiple PROs at 4 time points (enrollment, 6 weeks, 3 months, 6 months). Factors associated with receipt of assistance were assessed with bivariate and multivariate analyses. Results: The study included 541 adults (range 70-96 years, 49% female, mixed incurable cancer diagnoses). Twenty-eight percent (153/541) received assistance completing PROs. Of these, 42% received assistance from caregivers, 37% from research staff, and 15% from both. Factors associated with receiving assistance included older age [Adjusted Odds Ratio (AOR) 3.71, 95% Confidence Interval (CI) 1.03-13.38], lower education level (3.92, 2.11-7.29), impaired cognition (1.90, 1.23-2.93), impaired functional status (2.16, 1.33-3.52), and impaired hearing (1.38, 1.05-1.80). Eighty percent of individuals who received assistance were identified at study initiation. Receiving assistance decreased over time from 28% to 18%, partially due to drop-outs. Conclusion: Over a quarter of older adults with advanced cancer in this study received assistance completing PROs. Completing PROs is a key aspect of many clinical programs and cancer trials; assistance in completing PROs should be offered and provided.