BACKGROUND: The 5-factor modified Frailty Index (mFI-5), which is the latest version of the Frailty Index, is a tool that calculates the risk of complications after treatment by scoring the comorbidity status of the patient. The aim of this study was to evaluate the efficacy of the mFI-5 in predicting complications in geriatric patients with an ankle fracture. METHODS: A retrospective examination was made of a total of 94 patients aged >65 years who were treated for an ankle fracture in our hospital between 2015 and 2020. Weber type A, B, and C fractures were included in the study. For each patient, the mFI-5 was calculated for the comorbidity status of diabetes, chronic obstructive pulmonary disease, congestive heart failure, hypertension requiring drugs, and non-independent functional status. Multivariance logistic regression analysis was used to evaluate the mFI-5 points as a predictor of negative outcomes. RESULTS: The mFI-5 was observed to be effective in the prediction of the complications of hospital re-admission, wound site infec- tion, life-threatening medical complications, and the presence of any complication (p<0.05). In the prediction of whether or not there was any complication, the mFI-5 was determined to be a more effective tool than body mass index, American Society of Anesthesiol- ogist, age, length of stay in hospital, and duration of operation (p<0.05, OR=2.726, 95% Confidence Interval=1.285–5.783). CONCLUSION: The mFI-5 is a sensitive tool for the prediction of complications which may develop following geriatric ankle frac- ture. The five comorbidities which constitute the mFI-5 are easily obtained from the patient anamnesis, and this renders it a practical clinical tool to identify high-risk patients, determine the preoperative risks, and improve the health-care service.