Little is known about factors that influence willingness to engage in treatment for attention deficit/hyperactivity disorder (ADHD).  From 2007 to 2008, in the context of a longitudinal study assessing ADHD detection and service use in the United States, we simultaneously elicited ADHD treatment perceptions from four stakeholder groups: adolescents, parents, health care professionals and teachers.  We assessed their willingness to use ADHD interventions and views of potential undesirable effects of two pharmacological (short- and long-acting ADHD medications) and three psychosocial (ADHD education, behaviour therapy and counselling) treatments.  In multiple regression analysis, willingness was found to be significantly related to respondent type (lower for adolescents than adults), feeling knowledgeable, and considering treatments acceptable and helpful, but not significantly associated with stigma/embarrassment, respondent race, gender and socioeconomic status.  Because conceptual models of undesirable effects are underdeveloped, we used grounded theory method to analyse open-ended survey responses to the question: 'What other undesirable effects are you concerned about?'  We identified general negative treatment perceptions (dislike, burden, perceived ineffectiveness) and specific undesirable effect expectations (physiological and psychological side effects, stigma and future dependence on drugs or therapies) for pharmacological and psychosocial treatments.  In summary, findings indicate significant discrepancies between teens' and adults' willingness to use common ADHD interventions, with low teen willingness for any treatments.  Results highlight the need to develop better treatment engagement practices for adolescents with ADHD.