Frailty Index as a clinical measure of biological age in psychiatry

•Serious mental illnesses may be characterized by accelerated biological aging.•Frailty has been defined as “a condition in which the individual is in a vulnerable state at increased risk of adverse health outcomes and/or dying when exposed to a stressor”.•The assessment of frailty through the Frailty Index (FI), recently emerged as a reliable macroscopic indicator of biological age, is extensively performed in geriatrics and gerontology, but it has rarely been implemented in relation to mental health.•The FI quantifies functional negative health attributes and measures their cumulative effect, thus providing a useful estimate of the individual's biological age and risk profile.•The FI may be of relevance in the evaluation of age-related phenomena associated with mental health disturbances.