Background: Treatment for hypertension improves cardiovascular outcomes. Frailty may be present in older people treated for hypertension, but associates with adverse drug effects, potentially including falls resulting in fractures. We aimed to determine the association between baseline frailty and fractures in patients initiated on antihypertensive treatment. Methods: We conducted a retrospective cohort study using United Kingdom primary care data, including new users of first-line antihypertensives aged 65 years or over. We reported degree of frailty (fit, mild, moderate, severe) at antihypertensive initiation using the Electronic Frailty Index. We examined the association of frailty with fractures using multivariable Poisson regression, and assessed for interaction between antihypertensive class and frailty. Results: Of 113,779 patients aged 65 years or over who initiated on first-line antihypertensives, 49,634 patients (44%) were mildly or more frail. Over 4.1 years mean follow-up, 6567 (5.8%) experienced a fracture, with 3832 (58%) of these fractures occurring in frail people. Among those with severe frailty, doubling of fracture risk was observed after antihypertensive initiation, compared with fit people [adjusted rate ratio 2.26, 95% confidence interval (CI) 1.93–2.65]. Secondary analyses indicate this pattern was replicated for hip and arm fractures, and strongest for spine fractures, and the association between different types of antihypertensives and fractures varied by frailty (p = 0.004), being lower in moderately frail users of renin-angiotensin blockers compared with calcium channel blockers [rate ratio 0.81, 95% CI 0.71–0.94]. Conclusions: Frailty is common among older patients initiating first-line antihypertensive treatment, and was associated with an increased fracture rate. Awareness of this is important to encourage clinicians to consider risk of falls and fractures when treating hypertension.