Attention-deficit/hyperactivity disorder (ADHD) is the most recent diagnostic label used to describe a behavioural condition of which the essential features are developmentally inappropriate levels of inattention, impulsivity and overactivity. ADHD has attracted both controversy and attention from the professional and scientific community. However, little is known regarding the explanatory models (implicit theories) of health professionals or of their beliefs regarding the treatment of this condition, specifically the impact of diagnostic labelling on their decisions concerning treatment. This study manipulated the presence versus absence of the diagnostic label ‘ADHD’ in a vignette study describing the symptoms of this condition. The vignette was presented to professionals in the educational, mental health and allied health fields. After reading the vignette, participants were required to complete a questionnaire examining implicit beliefs concerning ADHD. The results confirmed that the presence of the diagnostic label (ADHD) changed the causal explanations by professional groups. However, the presence of the diagnostic label did not significantly change the beliefs about the optimal treatment strategy for this condition.