The term frailty denotes a multi-dimensional syndrome characterised by reduced physiological reserves and increased vulnerability. Frailty may be used as a marker of biological age, distinct from chronological age. There are several instruments for frailty assessment. The Clinical Frailty Scale (CFS) is probably the most commonly used in the acute care context. It is a 9-level scale, derived from the accumulated deficit model of frailty, which combines comorbidity, disability, and cognitive impairment. The CFS assessment is fast and easy to implement in daily clinical practice. The CFS is relevant for risk stratification, and may also be used as a screening instrument to identify frail patients suitable for further geriatric evaluation, i.e. a comprehensive geriatric assessment (CGA). By providing information on long-term prognosis, it may improve informed decision-making on an individual basis.