Use of the Revised NEO Personality Inventory (NEO-PI-R; Costa & McCrae, 1992) in adolescent samples has shown that a few respondents have difficulty with a subset of items. We identified 30 items that were not understood by at least 2% of adolescent respondents and 18 additional items with low item-total correlations, and we wrote 2 trial replacement items for each. We used self-report and observer rating data from 500 respondents aged 14 to 20 to select replacement items. The modified instrument retained the intended factor structure and showed slightly better internal consistency, cross-observer agreement, and readability (Flesch-Kincaid grade level = 5.3). The NEO-PI-3 appears to be useful in high school and college samples and may have wider applicability to adults as well.