The Five-Factor Personality Inventory (FFPI) assesses a person's position on the (Dutch) psycholexically based Big Five factors: Extraversion, Agreeableness, Conscientiousness, Emotional Stability, and Autonomy. FFPI factor scores are reliable and valid if ratings are made by adults. The present study yields preliminary evidence of whether young adolescents provide reliable and valid self-ratings on this instrument or whether this depends on their cognitive ability level. The sample consisted of a large and representative cohort of youngsters with a mean age of 13 years. The adult structure of the FFPI was generally well replicated, across all ability levels represented in the study. The findings further suggest that young adolescents' factor scores are construct-valid and sufficiently reliable to be used in (group) research settings. However, for reports on individual profiles and decision making, an adolescent's cognitive ability level would need to be rather high. Even then, measuring Autonomy seems challenging. (Contains 3 tables.)