BackgroundRoutinely collected clinical data based on electronic medical records could be used to define frailty.AimTo estimate the ability of four potential frailty measures that use electronic medical record data to identify older patients who were frail according to their GP.Design and settingThis retrospective cohort study used data from 36 GP practices in the Dutch PHARMO Data Network.MethodThe measures were the Dutch Polypharmacy Index, Charlson Comorbidity Index (CCI), Chronic Disease Score (CDS), and Frailty Index. GPs’ clinical judgement of patients’ frailty status was considered the reference standard. Performance of the measures was assessed with the area under the receiver operating characteristic curve (AUC). Analyses were done in the total population and stratified by age and sex.ResultsOf 31 511 patients aged ≥65 years, 3735 (11.9%) patients were classified as frail by their GP. The CCI showed the highest AUC (0.79, 95% confidence interval [CI] = 0.78 to 0.80), followed by the CDS (0.69, 95% CI = 0.68 to 0.70). Overall, the measures showed poorer performance in males and females aged ≥85 years than younger age groups (AUC 0.55–0.58 in females and 0.57–0.60 in males).ConclusionThis study showed that of four frailty measures based on electronic medical records in primary care only the CCI had an acceptable performance to assess frailty compared with frailty assessments done by professionals. In the youngest age groups diagnostic performance was acceptable for all measures. However, performance declined with older age and was least accurate in the oldest age group, thereby limiting the use in patients of most interest.