Intraindividual variability of physical status and affect/beliefs as well as their relations with cognition were examined in 3 groups of older adults: healthy elderly, individuals with a nonneurological health-related disturbance (arthritis) and people with neurological compromise (dementia). The findings showed that greater inconsistency in physical performance was observed in groups characterized by central nervous system dysfunction. By contrast, fluctuations in affect appeared to reflect other more transient sources, such as pain. In general, increased inconsistency in non-cognitive domains was associated with poorer cognitive function. There were cross-domain links between inconsistency in physical functioning and fluctuations in cognitive performance, although the nature of the links depended largely upon the neurological status of the individuals. Considered together, the result indicated that measures of cognitive as well as physical variability are important behavioral markers of neurological integrity. (JINS, 2002, 8, 893–906.)