Current knowledge about the validity of the psychopathy syndrome in youth is limited largely to studies relying on parent-teacher rating scales or slight modifications of adult measures. Recently, the Psychopathy Checklist: Youth Version (PCL:YV) was designed for use with adolescents. However, most studies that have used this measure examined incarcerated males and addressed only validity criteria related to antisocial behavior. We investigated the generality and construct validity of the psychopathy syndrome in an adolescent sample by assessing 115 adolescent males on probation with the PCL:YV. Reliability of measurement was high. PCL:YV ratings predicted not only antisocial behaviour but also other indices of childhood psychopathology, interpersonal behaviors associated with adult psychopathy, and a lack of attachment to parents. These findings suggest that the PCL:YV identifies a syndrome in adolescence consistent with theory and research on adult males.