Frailty is a common, heterogeneous, geriatric syndrome associated with adverse health events. Over the last years, a growing debate has emerged concerning the inclusion of cognitive impairment in the definition of frailty. In fact, cognitive impairment has been increasingly recognized as a potential contributor to the clinical vulnerability of older persons. This review presents key studies describing the interrelationships between cognition and frailty; in particular we examine the clinical relevance of cognitive impairment in the determination of the frailty syndrome.