There is increasing policy interest in the consideration of frailty measures (rather than chronological age alone) to inform a more equitable allocation of health and social care resources in the community. The Clinical Frailty Scale (CFS) has attracted interest for its simplicity and consideration of multiple relevant geriatric dimensions. However, a criticism of the CFS has been the possible subjectivity in the scoring, bringing the possible danger of lack of scoring consistency across agencies. For that reason, the authors of the CFS published a classification tree method to assist with routine scoring of the CFS.The aim of the present study was to apply the CFS classification tree to data from adults aged 65 and over from The Irish Longitudinal Study on Ageing (TILDA) and correlate derived CFS categories with patterns of health and social care utilisation in Irish older people assessed in Wave 5 of the study (year 2018). In addition, we explored how CFS categories and states changed over 8 years in TILDA between Wave 1 (2010) and Wave 5.Results showed the following prevalence of CFS categories in Wave 5: 6% ‘very fit’ (CFS1), 36% ‘fit’ (CFS2), 31% ‘managing well’ (CFS3), 16% ‘vulnerable’ (CFS4), 6% ‘mildly frail’ (CFS5), 4% ‘moderately frail’ (CFS6) and 1% ‘severely frail’ (CFS7). No participants were ‘very severely frail’ or ‘terminally ill’. In wave 5, increasing CFS categories had an association with increasing utilisation of hospital and community health services, and increasing hours of formal and informal social care provision. The transitions analyses from Wave 1 to 5 suggested a dynamic picture of CFS transitions, 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.Our results suggest that the CFS classification tree was able to stratify the TILDA population aged 65 and over into subgroups with increasing health and social care needs. The CFS classification tree could be used to aid the allocation of health and social care resources in older people in Ireland, but given the frequency of CFS transitions in the population, it is recommended that CFS status in individuals is reviewed at least every 2 years.