The authors examined siblings' dyadic and differential experiences of parental warmth from 7 to 19 years of age. Participants were first- and second-borns from 201 families who reported on their warmth with each parent in 4 home interviews spaced over 5 years. Supporting an individual development hypothesis, multilevel model analyses revealed declines in parental warmth from early through midadolescence but no changes or increases in warmth in middle childhood and later adolescence. Consistent with a learning-from-experience hypothesis, declines in paternal warmth were less pronounced for second-borns than for firstborns. The results also suggest gender intensification in differential warmth for parents of mixed-gender sibling dyads. Within-family comparisons of youth provide unique insights about family relationship development.