The enduring nature of personality, particularly in adulthood, has been demonstrated in numerous cross-sectional and longitudinal studies where high stability has been observed even with decades between testing intervals. Biometrical studies, reporting genetic eects as the primary cause of familial resemblance, have been interpreted as lending further support to theories concerning an inherent stability of personality. Heterogeneity in heritability estimates across age cohorts may, however, alter this notion. Furthermore, recent phenotypic studies report some evidence for change over the life course for characteristics such as `outgoingness'. The purpose of the present analysis was to examine longitudinal stability and change in the sources of variation in personality in the latter half of the life-span using a twin/adoption design with up to four times of measurement. Data from the Swedish Adoption/Twin Study of Aging (SATSA) are used both to demonstrate how genetic and environmental eects can contribute to phenotypic stability, and to estimate the extent to which these in¯uences are, themselves, stable. Particularly intriguing are ®ndings of increasing variability in rate of change despite relative mean level stability as well as genetic stability.