Cognitive change in the elderly can be due to several etiological factors which are empirically difficult to separate and clinically problematic to differentiate. Normal aging is accompanied by behavioral slowing. The slowing down of psycho-motor processes results in a lowered intelligence quotient, but cannot be taken as unequivocal evidence for intellectual deterioration. Acuity of abstract non-verbal reasoning diminishes with the normal aging process, but generalizations from this evidence cannot be made without several qualifications. Dementia is a pathological process which often accompanies normal aging, is apparently physiological in origin, and is psychometrically characterized by impairment of memory and abstract verbal reasoning. Although certain post-mortem findings are associated with dementia, the severity of these physiological factors is not related to the degree of pre-mortem intellectual deterioration in a straightforward fashion. The conceptualization of dementia is unduly confused by artificial division into several subtypes. Finally, depression, a common concomitant of both the normal aging and dementing process, can result in psychomotor retardation, memory and concentration impairment, and a host of other idiosyncratic alterations of cognition. The configuration, rather than the severity of cognitive alterations, can best be used in differential diagnosis and treatment formulations, as well as in future research. (Author/NRB)