INTRODUCTION: Hip and knee arthroplasties are the most common planned orthopedic surgical procedures in older persons. It would be useful to identify frailties before surgery to improve the outcome of older patients.PURPOSE: The objective of this work was to identify the criteria of a simplified comprehensive geriatric assessment (mini-CGA) that were associated with unplanned hospital readmission and postoperative complications within 3 months after the planned hip and/or knee arthroplasty in patients ≥ 65 years.METHODS: This prospective study was carried out in the orthopedic department of Marseille University Hospital from January to May 2019. A mini-CGA was performed preoperatively.RESULTS: One hundred four patients were included in the study. The rate of early readmission within 3 months after surgery was 12.5% and the rate of postoperative complications was 40.4%. In multivariate analysis, dependence in the activities of daily living (ADL ≤ 5) was the only factor associated with unplanned readmission (aOR = 9.9, 95% CI 1.9-50.8), and living alone was the only factor associated with postoperative complications (aOR = 3.2, 95% CI 1.2-8.8).CONCLUSIONS: We found that the ADL score was associated with the risk of unplanned readmission in older patients undergoing planned arthroplasty, and that living alone was associated with postoperative complications. A preoperative mini-CGA appears essential to limit postoperative morbidity.