The present article examines Big Five personality development across adolescence and middle adulthood. Two adolescents and their fathers and mothers from 285 Dutch families rated their own and their family members' personality. Using accelerated longitudinal growth curve analyses, mean level change in Big Five factors was estimated. For boys, Extraversion and Openness decreased and for girls, Extraversion, Agreeableness, Conscientiousness, and Openness increased. Whereas mothers' Emotional Stability and Conscientiousness increased, fathers' Extraversion, Agreeableness, and Emotional Stability decreased. Differences in self- and other-reported personality change were found, as well as interindividual differences in personality change. Results confirm that personality change is possible across the life course but these changes are not similar for all individuals and depend on the type of observer. Copyright © 2006 John Wiley & Sons, Ltd.