Objective: To assess whether frailty in acutely admitted older medical patients, assessed by a self-report questionnaire and evaluation of functional level at discharge, was associated with readmission or death within 6 months after discharge. A second objective was to assess the predictive performance of models including frailty, functional level, and known risk factors. Methods: A cohort study including acutely admitted older patients 65+ from seven medical and two acute medical units. The Tilburg Frailty Indicator (TFI), Timed-Up-and-Go (TUG), and grip strength (GS) exposure variables were measured. Associations were assessed using Cox regression with first unplanned readmission or death (all-causes) as the outcome. Prediction models including the three exposure variables and known risk factors were modelled using logistic regression and C-statistics. Results: Of 1328 included patients, 50% were readmitted or died within 6 months. When adjusted for gender and age, there was an 88% higher risk of readmission or death if the TFI scores were 8–13 points compared to 0–1 points (HR 1.88, CI 1.38;2.58). Likewise, higher TUG and lower GS scores were associated with higher risk of readmission or death. The area under the curve for the prediction models ranged from 0.64 (0.60;0.68) to 0.72 (0.68;0.76). Conclusion: In acutely admitted older medical patients, higher frailty assessed by TFI, TUG, and GS was associated with a higher risk of readmission or death within 6 months after discharge. The performance of the prediction models was mediocre, and the models cannot stand alone as risk stratification tools in clinical practice.