<b>Background:</b> There is increasing policy interest in the consideration of frailty measures (rather than chronological age alone) to inform more equitable allocation of health and social care resources. In this study the Clinical Frailty Scale (CFS) classification tree was applied to data from The Irish Longitudinal Study on Ageing (TILDA) and correlated with health and social care utilisation. CFS transitions over time were also explored. <b>Methods:</b> Applying the CFS classification tree algorithm, secondary analyses of TILDA data were performed to examine distributions of health and social care by CFS categories using descriptive statistics weighted to the population of Ireland aged ≥65 years at Wave 5 (n=3,441; mean age 74.5 (SD ±7.0) years, 54.7% female). CFS transitions over 8 years and (Waves 1-5) were investigated using multi-state Markov models and alluvial charts. <b>Results</b>: The prevalence of CFS categories at Wave 5 were: 6% 'very fit', 36% 'fit', 31% 'managing well', 16% 'vulnerable', 6% 'mildly frail', 4% 'moderately frail' and 1% 'severely frail'. No participants were 'very severely frail' or 'terminally ill'. Increasing CFS categories were associated with increasing hospital and community health services use and increasing hours of formal and informal social care provision. The transitions analyses suggested CFS transitions are dynamic, with 2-year probability of transitioning from 'fit' (CFS1-3) to 'vulnerable' (CFS4), and 'fit' to 'frail' (CFS5+) at 34% and 6%, respectively. 'Vulnerable' and 'frail' had a 22% and 17% probability of reversal to 'fit' and 'vulnerable', respectively. <b>Conclusions:</b> Our results suggest that the CFS classification tree stratified the TILDA population aged ≥65 years into subgroups with increasing health and social care needs. The CFS could be used to aid the allocation of health and social care resources in older people in Ireland. We recommend that CFS status in individuals is reviewed at least every 2 years.