A series of studies investigated White U.S. 3- and 4-year-old children's use of gender and race information to reason about their own and others’ relationships and attributes. Three-year-old children used gender- but not race-based similarity between themselves and others to decide with whom they wanted to be friends, as well as to determine which children shared their own preferences for various social activities. Four-year-old (but not younger) children attended to gender and racial category membership to guide inferences about others’ relationships but did not use these categories to reason about others’ shared activity preferences. Taken together, the findings provide evidence for three suggestions about these children's social category-based reasoning. First, gender is a more potent category than race. Second, social categories are initially recruited for first-person reasoning but later become broad enough to support third-person inferences. Finally, at least for third-person reasoning, thinking about social categories is more attuned to social relationships than to shared attributes. (Contains 3 tables and 5 figures.)