The number of older people with complex clinical conditions and complex care needs continues to increase in the population. This is presenting many challenges to healthcare professionals and healthcare systems. In the face of these challenges, approaches are required that are practical and feasible. The frailty paradigm may be an excellent opportunity to review and establish some of the principles of comprehensive Geriatric Assessment in specialties outside Geriatric Medicine. The assessment of frailty using Frailty Indexes provides an aid to the 'situational diagnosis' of complex clinical situations, and may help in tackling uncertainty in a person-centred approach.