A polymorphism (Val 158 Met) in the gene for catechol-O-methyl transferase (COMT) was previously associated with differences in cognitive ability and personality. Here we examine associations between this polymorphism and cognitive ability, cognitive aging, personality and mood in 460 relatively healthy people born in 1921. All had cognitive ability measured at age 11 in the Scottish Mental Survey of 1932, and again at age 79. COMT genotype was not associated with childhood IQ. At age 79, COMT genotype was significantly related to differences in verbal declarative memory (scores on the Logical Memory test; p=0.028) and to scores on the personality trait of intellect/imagination (p=0.023), adjusted for sex and childhood IQ. In both cases the Val/Met heterozygotes had higher scores than both homozygous groups. There were trends toward the heterozygotes having higher scores on the personality traits of agreeableness and conscientiousness. The effect of COMT genotype on Logical Memory scores was independent of the effect of APOE genotype, and similar in effect size. Therefore, COMT genotype may contribute to differences in normal cognitive aging and to differences in some of the major personality traits in old age.