BACKGROUND: routine frailty identification and management is national policy in England, but there remains a lack of evidence on the impact of frailty on healthcare resource use. We evaluated the impact of frailty on the use and costs of general practice and hospital care. METHODS: retrospective longitudinal analysis using linked routine primary care records for 95,863 patients aged 65-95 years registered with 125 UK general practices between 2003 and 2014. Baseline frailty was measured using the electronic Frailty Index (eFI) and classified in four categories (non, mild, moderate, severe). Negative binomial regressions and ordinary least squares regressions with multilevel mixed effects were applied on the use and costs of general practice and hospital care. RESULTS: compared with non-frail status, annual general practitioner consultation incidence rate ratios (IRRs) were 1.24 (95% CI: 1.21-1.27) for mild, 1.41 (95% CI: 1.35-1.47) for moderate, and 1.52 (95% CI: 1.42-1.62) for severe frailty. For emergency hospital admissions, the respective IRRs were 1.64 (95% CI 1.60-1.68), 2.45 (95% CI 2.37-2.53) and 3.16 (95% CI: 3.00-3.33). Compared with non-frail people the IRR for inpatient days was 7.26 (95% CI 6.61-7.97) for severe frailty. Using 2013/14 reference costs, extra annual cost to the healthcare system per person was £561.05 for mild, £1,208.60 for moderate and £2,108.20 for severe frailty. This equates to a total additional cost of £5.8 billion per year across the UK. CONCLUSIONS: increasing frailty is associated with substantial increases in healthcare costs, driven by increased hospital admissions, longer inpatient stay, and increased general practice consultations.