It is now presumed that youth do not move directly from adolescence to adulthood, but rather pass through a transitional period, "emerging adulthood." The Revised Inventory of the Dimensions of Emerging Adulthood (IDEA-R) is a self-report instrument developed to examine the attributes of this period. "At-risk" youth appear to enter emerging adulthood developmental tasks at a slightly earlier age than general population youth. In the present study, a 21-item version of the IDEA was administered to a sample of 1676 "at-risk" continuation (alternative) high school students in Southern California. Principal component factor analysis with orthogonal rotation revealed three factors the authors labeled "Identity Exploration," "Experimentation/Possibilities," and "Independence." Overall, the measure demonstrated high internal consistency. Construct validity analyses indicated that the measure was correlated with demographics, risk behaviors, and psychological measures. The authors conclude that the IDEA-R is a useful instrument for measuring emerging adulthood in at-risk populations.