This investigation examined the normative expectation that adult children should be responsible for the care of their aging parents, and how this norm changes over the adult life span, across several decades of historical time, in relation to generational position in families, and between successive generations. Analyses were performed using 4 waves of data from the University of Southern California (USC) Longitudinal Study of Generations between 1985 and 2000. A multilevel latent growth model was estimated using 4,527 observations from 1,627 individuals nested within 333 families. Results revealed that filial norms weakened after midlife, in response to parental death, and over historical time, yet strengthened in later-born generations. Findings are discussed in terms of the malleability of filial responsibility over the life course.