Background: Research indicates that diabetes mellitus (DM) may be a risk factor for frailty and individuals with DM are more likely to be frail than individuals without DM; however, there is limited research in hospitalised older adults.Objectives: To determine the extent of frailty in hospitalised older adults with and without DM using a 16-item Frailty Risk Score (FRS) and assess the role of frailty in predicting 30-day rehospitalisation, discharge to an institution and in-hospital mortality.Methods: The study was a retrospective, cohort, correlational design and secondary analysis of a data set consisting of electronic health record data. The sample was older adults hospitalised on medicine units. Logistic regression was performed for 30-day rehospitalisation and discharge location. Cox proportional hazards regression was used to analyse time to in-hospital death and weighted using propensity scores.Results: Of 278 hospitalised older adults, 49% had DM, and the mean FRS was not significantly different by DM status (9.6 vs. 9.1, p = 0.07). For 30-day rehospitalisation, increased FRS was associated with significantly increased odds of rehospitalisation (AOR = 1.24, 95% CI [1.01, 1.51], p = 0.04). Although 81% were admitted from home, 57% were discharged home and 43% to an institution. An increased FRS was associated with increased odds of discharge to an institution (AOR = 1.48, 95% CI [1.26, 1.74], p Conclusion: Diabetes mellitus and frailty were highly prevalent; the mean FRS was not significantly different by DM status. Although increased frailty was significantly associated with rehospitalisation and discharge to an institution, only DM was significantly associated with in-hospital mortality.Relevance to clinical practice: Frailty assessment may augment clinical assessment and facilitate tailoring care and determining optimal outcomes in patients with and without DM