Objectives.The effect of occupational characteristics on cognitive change over 20 years was examined.Method.Occupational characteristics-intellectual challenge, physical hazards, and psychological demands-were assessed in the Glostrup 1914 Cohort when aged 60 years, and cognitive ability was assessed by 4 cognitive ability tests at ages 60, 70, and 80. RESULTS: Individuals in more intellectually challenging occupations had higher cognitive ability (r = .27-.38, p <.01), whereas those in more physically hazardous occupations performed more poorly (r = -.12 and -.13 at ages 50 and 60, p <.05). In growth curve models, intellectual challenge continued to be associated with cognitive ability, controlling for sex, education, and social class. However, the association was reversed after accounting for cognitive ability at age 50; of 2 individuals with the same baseline level of cognitive ability, the one in the more intellectually challenging occupation had lower subsequent cognitive ability. The association of physical hazards with lower cognitive ability level did not remain after adjustment for the basic demographics, and none of the occupational characteristics were associated with cognitive change between age 60 and 80.Discussion.Notwithstanding the reversal of the effect of occupational intellectual challenge on cognitive ability level after accounting for pre-exiting cognitive differences, there was no evidence for long-term effects of occupational characteristics on cognitive change in old age.