Health-related quality of life (HRQoL) is highly valued among older adults with cancer. The Geriatric 8screening tool identifies individuals with frailty, but its association with HRQoL remains sparsely investigated. Herein, we evaluate whether Geriatric 8frailty is associated with short-term and long-term HRQoL in older patients with cancer. In this Danish single-centre, prospective cohort study, patients aged 70years and older, referred to oncological assessment for solid cancers, were screened with the Geriatric 8. Patients completed the European Organisation for Research and Treatment of Cancer (EORTC) Quality-of-Life Core 30 (QLQ-C30) and Elderly 14(ELD14) questionnaires at baseline, 3months, 6months, 9months, and 12months. Patient characteristics were obtained from medical records. Differences in mean global health status and QoL (GHS), measured using the two seven-point Likert scale questions from the EORTC QLQ-C30 regarding overall health and QoL during the past week, between patients with frailty (defined as a Geriatric 8score of ≤14) and without frailty within 12months were the primary outcome. Secondary outcomes were differences in the mean EORTC Summary Score comprised of all questions from the QLQ-C30 except for those included in the GHS and a question concerning financial difficulties, and five functional (physical, role, and social functioning, maintaining purpose, and family support from the EORTC QLQ-C30 and the EORTC-QLQ-ELD14), and five symptom scales (fatigue, pain, mobility, future worries, and burden of illness from the EORTC-QLQ-C30 and the EORTC-QLQ-ELD14). Analyses were done using linear mixed models. All primary and secondary outcomes were adjusted for gender, treatment intent, and cancer type and the primary outcome was also assessed by means of a responder analysis. Between June 1, 2020and Oct 15, 2021, 1398eligible patients were screened with the Geriatric 8 (908 [65%] with frailty and 490 [35%] without frailty) and provided medical record data. Of these patients, 707 (51%) also provided HRQoL data (437 [62%] with frailty and 270 [38%] without frailty). When adjusted, patients with frailty had poorer GHS(-15·1, 95% CI -18·5to -11·6; p<0·0001) at baseline and throughout follow-up (3 months -7·4, -11·0to -3·7, p=0·0001; 6months -11·7, -15·5to -7·9, p<0·0001; 9months -10·4, -14·3to -6·5, p<0·0001; 12months -10·4, -14·6to -6·2, p<0·0001) compared to patients without frailty. Adjusted summary scores were also poorer for patients with frailty (-9·9, 95% CI -12·1to -7·6; p<0·0001) compared to patients without frailty at baseline and throughout follow-up (3 months -8·2, -10·5to -5·8, p=0·0001; 6months -9·0, -11·4to -6·6, p<0·0001; 9months -9·2, -11·7to -6·8, p<0·0001; 12 months -8·9, -11·5to -6·3, p<0·0001). Patients with frailty had significantly worse physical and role functioning, mobility, and fatigue outcomes, with no differences in family support within 12months, at all timepoints. Older patients with cancer and frailty have significantly poorer HRQoL than those without frailty within the 12months following an oncology referral. Thus, by identifying and treating frailty, we can ultimately improve patient HRQoL. The Danish Cancer Society, Academy of Geriatric Cancer Research (AgeCare), Odense University Hospital, University of Southern Denmark, Dagmar Marshalls Fond, and Agnes and Poul Friis Fond.