A substantial proportion of adolescents with attention deficit hyperactivity disorder (ADHD) do not appropriately adhere to prescribed treatments, especially to pharmacological treatments. It is important to disentangle the specific attitudes that contribute to treatment adherence. A 33-item questionnaire was applied to 120 adolescents diagnosed with ADHD and their respective parents. Reliability of the scale was explored using factor analysis, Cronbach's alpha, and test-retest. Validity was explored by face validity and the known-groups method. For the young people's version, three main dimensions (preoccupations, insight and self-concept) emerged. The parents' version showed six main dimensions (child's personal attitudes, worries, social stigma, insight, future side effects and knowledge). The potential of this questionnaire to explore the attitudes of patients and their families towards treatments and for clinicians to predict treatment adherence is discussed.