The stability of sex-typed behavior from the preschool to the middle school years was examined. The Preschool Activities Inventory, a measure of within-sex variation in sex-typed behavior, was completed by the primary caregiver when the child was 2.5, 3.5, and 5 years, and a modified version, the Child Activities Inventory, was completed by the child at age 8. The investigation involved a general population sample of 2,726 boys and 2,775 girls. Sex-typed behavior increased through the preschool years, and those children who were the most sex typed at age 2.5 were still the most sex typed at age 5, with those children who showed the highest levels of sex-typed behavior during the preschool years continuing to do so at age 8.