This study examined factors that predicted children's gender intergroup attitudes at age 5 and the implications of these attitudes for intergroup behavior. Ethnically diverse children from low-income backgrounds (N = 246; Mexican-, Chinese-, Dominican-, and African American) were assessed at ages 4 and 5. On average, children reported positive same-gender and negative other-gender attitudes. Positive same-gender attitudes were associated with knowledge of gender stereotypes. In contrast, positive other-gender attitudes were associated with flexibility in gender cognitions (stereotype flexibility, gender consistency). Other-gender attitudes predicted gender-biased behavior. These patterns were observed in all ethnic groups. These findings suggest that early learning about gender categories shape young children's gender attitudes and that these gender attitudes already have consequences for children's intergroup behavior at age 5.