This study was designed to refine and validate a 160-item self-report instrument which drew its items from personality theories and from clinical practice related to delinquency. The aim was to estimate the usefulness of items descriptive of delinquent behavior by testing their reliability and discriminative power. There were two objectives. First: to test a set of items for their power to discriminate delinquent from non-delinquent responses which referred to delinquent and nondelinquent behavior. Second, to validate the power of the selected set of items to discriminate delinquent from non-delinquent youths in a second mixed group. Both objectives were realized in that significantly discriminating items emerged, which when administered to a second group, correctly classified 80% of the tested youths. The subjects in this study were youths who were selected as delinquents (n = 125) and nondelinquents (N = 125). The items used in the measuring instrument were collected over a period of several. years and based on theoretic al and clinical resources. Selected items referred to family togetherness, family supportiveness, limit-setting and behavior consequences, self-esteem and success, and school functioning. The results of the study provide a set of items which may be administered to help describe dis social behavior. The items may be used to educate parents, other adults, and students in recognizing some psycho-social behaviors related to interpersonal social behavior.