The rate of cognitive decline in Alzheimer's disease (AD) varies considerably between individuals, with some subjects showing substantial deterioration and others showing little or no change over the course of the disease. These wide variations support the relatively new concept of Rapid Cognitive Decline (RCD). Patients with an accelerated rate of cognitive decline have showed to present a worse evolution in terms of mortality, loss of autonomy and institutionalisation. The conclusions from RCD studies conducted in the past years remain very heterogeneous and sometimes contradictory. This is possibly due to methodological differences, mainly the different "a priori" definitions of RCD used to identify rapid decliners. Consequently of this, there is considerable variation in reported frequency of patients with RCD which may vary from 9.5% to 54%. The lack of both consensus definition and consensual clinical assessment tools is one of the major barriers for establishing an appropriated management of rapid decliners in clinical practice. Presently, management of rapid decliners in AD remains to be a challenge waiting to better know predictive factors of a RCD. To date no specific guidelines exist to follow-up or to treat patients with this condition. This consensus paper proposes the loss of 3 points or greater in Mini-Mental State Examination (MMSE) during six months as an empirical definition of rapid cognitive decline to be used in routine medical practice and to be relevant for clinical-decision making in patients with mild to moderately-severe AD.