Research on personality and adiposity has focused primarily on middle‐aged and older adults. The present research sought to (a) replicate these associations in a young adult sample, (b) examine whether sex, race, or ethnicity moderate these associations, and (c) test whether personality is associated with the subjective experience of body weight and discrepancies between perceived and actual weight. Participants (N = 15,669; Mage = 29; 53% female; ∼40% ethnic/racial minority) from Wave 4 of the National Longitudinal Study of Adolescent Health completed a Five‐Factor Model personality measure and reported their weight, height, and perception of weight category (e.g., overweight); trained staff measured participants’ height, weight, and waist circumference. Conscientiousness was associated with healthier weight, with a nearly 5 kg difference between the top and bottom quartiles. Neuroticism among women and Extraversion among men were associated with higher adiposity. Neuroticism was also associated with misperceived heavier weight, whereas Extraversion was associated with misperceived taller and leaner. The associations were similar across race/ethnic groups. Personality is associated with objective and subjective adiposity in young adulthood. Although modest, the effects are consistent with life span theories of personality, and the misperceptions are consistent with the conceptual worldviews associated with the traits.