This study used the correlated trait–correlated method minus one model to examine the convergent and discriminant validity of the scales of the Strengths and Difficulties Questionnaire (SDQ). The SDQ scales are emotional symptoms (ES), conduct problems (CP), hyperactivity (HY), peer problems (PP), and prosocial behaviors (PS). A total of 202 adolescents provided self-ratings and were also rated by their mothers and teachers. The findings indicated support for convergent validity for all five SDQ scales for all three respondents. Generally there was more convergence between mother–adolescent ratings than mother–teacher and adolescent–teacher ratings, especially for ES and PP. There was support for the discriminant validity between the traits in all scales, except between CP and HY. The findings are discussed in relation to the construct validity and clinical use of the SDQ.