Résumé : Objectives: The aim of this study is to describe a large-scale, Belgian implementation project about geriatric assessment (=GA) in daily oncology practice and to identify barriers and facilitators for implementing GA in this setting. Design / setting / participants: The principal investigator of every participating hospital (n=22) was invited to complete a newly developed questionnaire with closed- and open-ended questions. The closed-ended questions surveyed how GA was implemented. The open-ended questions identified barriers and facilitators for the implementation of GA in daily oncology practice. Descriptive statistics and conventional content analysis were performed as appropriate. Results: Qualifying criteria (e.g. disease status and cancer type) for GA varied substantially between hospitals. Thirteen hospitals (59.1%) succeeded to screen more than half of eligible patients. Most hospitals reported that GA data and follow-up data had been collected in almost all screened patients. Implementing geriatric recommendations and formulating new geriatric recommendations at the time of follow-up are important opportunities for improvement. The majority of identified barriers were organizational, with high workload, lack of time or financial/staffing problems as most cited. The most cited facilitators were all related to collaboration. Conclusion: Interventions to improve the implementation of GA in older patients with cancer need to address a wide range of factors, with organization and collaboration as key elements. All stakeholders, seeking to improve the implementation of GA in older patients with cancer, should consider and address the identified barriers and facilitators.