Summary <p>Diabetes increases fracture risk, but whether this risk varies by age at diagnosis is unclear. In a large cohort of Australian women, younger age at diabetes diagnosis was linked to substantially higher fracture risk. Age at diagnosis may enhance fracture risk assessment and guide targeted prevention.</p> Purpose <p>The purpose is to examine whether age at diabetes diagnosis modifies the association between diabetes and fracture risk in women.</p> Methods <p>We used data from 12,170 participants in the 1946–1951 cohort of the Australian Longitudinal Study on Women’s Health, linked with administrative health records. Women were followed from age 27 to 76&#xa0;years. Diabetes status, age at diagnosis, and fracture events were identified from survey and administrative data. Poisson regression was used to compare fracture rates between women with and without diabetes, stratified by age at diagnosis, and adjusted for age and time-varying BMI.</p> Results <p>A total of 2251 women (18.5%) had diabetes and 3761 (30.9%) sustained at least one fracture. Compared to women without diabetes, those with diabetes had a higher fracture risk (RR 1.13; 95% CI 1.02–1.24). The excess risk varied by age at diagnosis: RR 1.61 (95% CI 1.23–2.12) for diagnosis at age 35, declining to RR 1.02 (95% CI 0.90–1.16) for diagnosis at age 60.</p> Conclusions <p>Diabetes is associated with increased fracture risk, but this risk varies by age at diagnosis. Women diagnosed at younger ages face substantially higher risk, while those diagnosed later show little excess risk. Age at diagnosis may improve fracture risk assessment and inform prevention.</p>