The purpose of this paper was to construct, refine, and test a measure of adolescent peer susceptibility. Current conceptualizations of peer susceptibility largely are one dimensional and include at most one or two domains of psychosocial functioning. In addition, most assessments of peer susceptibility are situation- or behavior-specific, thus limiting their generalizability. These problems and concerns seriously limit our understanding of the precise psychosocial mechanisms through which peer relations influence adolescent identity formation. For the present student, adolescent focus groups provided self-generated, open-ended responses to yield an ecologically valid framework for constructing self-report items assessing peer susceptibility. Analysis of the data indicated that peer susceptibility is multidimensional and consists of seven dimensions reflecting conformity self-efficacy; personal control; decision-making skills; self-derogation; social comparison; social confidence; and assertive skills. Multiple group comparisons indicated that males and females differed significantly in the magnitude of the relation between social and cognitive susceptibility. Implications highlight the use of a theoretically guided, psychometrically valid and reliable assessment of peer susceptibility for screening highly vulnerable youth where indicated. Appendixes include: Sample Prompts Used in Focus Groups, Introductory Statement Read to Participants, Adolescent Peer Susceptibility Scale, and Summary of Statistics and Psychometric Properties for Adolescent Peer Susceptibility Items. (Contains 4 appendixes, 2 figures, 9 tables, and 92 references.) (Author/JDM)