Parental differential treatment has been linked to individual well-being and sibling relationship quality in childhood, adolescence, and middle adulthood but has not been examined in young adulthood. Data were collected from 151 pairs of young adult siblings (N = 302, M age = 23.90, SD = 5.02). Two siblings in each family reported on treatment from mothers and fathers, depressive symptoms, and sibling relationship quality. Using multilevel modeling, analyses examined the role of favoritism and the magnitude of differential treatment from both mothers and fathers. Offspring who reported receiving less support relative to their sibling (i.e., less favored) reported more depressive symptoms. Greater amounts of differential treatment were associated with less sibling intimacy. Several associations, however, varied by parent gender, sibling gender composition, and the magnitude of differential treatment. The results suggest that favoritism and magnitude of differential treatment from both mothers and fathers are salient in young adulthood.