Research has shown that mothers often differentiate among their adult children in terms of closeness and support; however, studies have not addressed why some mothers report preferences among children and others do not. To distinguish between mothers who do and do not report favouring some of their adult children, we used data from a within-family study in which 553 older mothers were interviewed about each of their children. Almost all of the mothers reported differentiating among their children regarding emotional closeness, confiding, or preference among caregivers. Multivariate analyses revealed that mothers' values and mother-child value similarity predicted which mothers differentiated among their children regarding closeness and confiding, whereas mothers' and children's demographic characteristics predicted which mothers differentiated regarding preferred caregivers. Black mothers were less likely than white mothers to differentiate when seeking a confidant; however, race played no role in mothers' likelihood of differentiating regarding emotional closeness or help during illness. Taken together, these findings indicate that differentiating among adult children is common; further, family-level predictors of mothers' differentiating mirror the patterns shown in dyad-level analyses of mothers' favouritism. (Contains 4 tables.)