This study administered the NEO Personality Inventory-3 (NEO-PI-3), a more readable version of an adult measure of the Five-Factor Model, to 449 boys and girls aged 12 and 13, who described themselves or a peer. Analyses of readability, reliability, factor structure, and convergent and discriminant validity suggested that the NEO-PI-3 can be appropriately used in this age group. Personality traits in children of this age closely resemble in structure and functioning the traits of older adolescents and adults. Most gender differences known from studies of adults are found in this age group, and mean levels show continuity with older groups. The NEO-PI-3 appears to be a useful instrument for research, and potentially for clinical applications, in middle-school-aged children.