Objective: To investigate beliefs and attitudes of the public toward attention deficit hyperactivity disorder (ADHD) in children and adults. Method: In a representative population survey in Germany ( N = 1,008) using computer-assisted telephone interviews, we asked participants about causal beliefs, illness recognition, treatment recommendations, and beliefs about ADHD, presenting an unlabelled vignette of a child or an adult with ADHD. Results: The most frequently endorsed causal beliefs for the depicted child with ADHD were “TV or Internet,” “lack of parental affection,” and “broken home.” In comparison with the child vignette, biological causal beliefs were endorsed more often after the adult vignette. In the child vignette, 66% advised against a treatment with stimulant medication. About 90% of respondents had heard of ADHD. Of those, 20% said they believed ADHD to be not a real disease. Conclusion: Beliefs of the German public partly contradict evidence and should be considered in therapeutical and public contexts.