The effects of age and dementia on Trail Making Test (TMT) performance were investigated in a sample of 765 participants in the Baltimore Longitudinal Study of Aging, 58 of whom met DSM-IIIR criteria for dementia and 40 dementia 'suspects,' who showed mild changes in one or two cognitive domains. Cross-sectional analyses of the 667 nondemented subjects whose ages ranged from 60 to 96, revealed significant age effects in completion times for both Parts A and B. Prevalence of errors increased with age on Part B, but not on Part A. Two-year longitudinal changes were examined in a subset of the sample (n = 385). Significant performance decrements for Part B, but not A, were found in completion times, with older age-groups showing the greatest slowing. Error rates did not increase. These findings suggest that the effects of age and aging are greater on TMT Part B than Part A. Dementia status accounted for a significant proportion of the variance in completion times after accounting for age effects. ROC analyses suggest that the TMT may be useful in screening for cognitive dysfunction. These findings underscore the effects of age and dementia on the TMT.