Background <p>Among older adults with acute illnesses, frailty is common and strongly associated with poorer prognosis. This study aimed to investigate the prevalence of pre-stroke frailty and its association with short-term functional outcomes in older patients with acute ischemic stroke (AIS).</p> Methods <p>We included consecutive AIS patients aged ≥ 60 years admitted to a hospital in Vietnam. Pre-stroke frailty was assessed using the modified Short Emergency Geriatric Assessment (mSEGA) frailty scale (score 0–8: not frail; score 9–11: frail; score 12–26: very frail). Short-term functional outcomes were evaluated using the modified Rankin Scale (mRS) at 30 days based on follow-up clinical assessments and interviews, with poor outcomes defined as mRS ≥ 3. The association between pre-stroke frailty and stroke outcomes was assessed using multivariable logistic regression analysis.</p> Results <p>A total of 304 participants (61.5% with mild and 38.5% with moderate stroke) were included, with a mean age of 78.0 ± 8.5 years, and 57.6% were female. The prevalence of pre-stroke frailty and very frailty was 30.6% and 32.2%, respectively. Multivariable logistic regression analysis demonstrated that pre-stroke very frail status remained an independent predictor of poor functional outcomes at 30 days, with an adjusted odds ratio (OR) of 3.29 (95% CI: 1.45–7.46, <i>p</i> = 0.004), after adjustment for age, sex, baseline NIHSS, and treatment strategy.</p> Conclusions <p>This study revealed a high prevalence of pre-stroke frailty among older patients with AIS in Vietnam. Pre-stroke very frail status was significantly associated with an increased risk of poor functional outcomes in this population.</p>