Using self-report measures, longitudinal studies in the US and cross-sectional studies from many cultures suggest that the broad factors of Neuroticism, Extraversion, and Openness to Experience decline from adolescence to adulthood, whereas Agreeableness and Conscientiousness increase. Data are inconsistent on the rate of change during adulthood, and on the generalizability of self-report findings to informant ratings. We analysed cross-sectional data from self-reports and informant ratings on the Revised NEO Personality Inventory in Czech (N = 705) and Russian (N = 800) samples. Some curvilinear effects were found, chiefly in the Czech sample; informant data generally replicated self-reports, although the effects were weaker. Although many of the details are not yet clear, there appear to be pan-cultural trends in personality development that are consistent with the hypothesis of intrinsic maturation. Copyright © 2004 John Wiley & Sons, Ltd.