The aim of the present study was to investigate the presence of attention deficit hyperactivity disorder (ADHD) in adult patients with severe dental anxiety. Specifically, we analysed the relationship among ADHD, oral health, and dental anxiety. The World Health Organization Adult ADHD Self-Report Scale (ASRS) Screener was administered to a consecutive sample of patients referred to a dental fear research and treatment clinic. Patients completed questionnaires measuring dental anxiety (Dental Fear Survey) and self-rated oral health, and underwent a full radiographic examination. Of the total sample (n = 110), 16% scored above the established ASRS cut-off point, which is indicative of having ADHD. The ADHD group showed a higher level of dental anxiety and poorer self-rated oral health. There were also indications of poorer clinical oral health in the ADHD group, but these results did not reach statistical significance. In conclusion, the results of this study indicate an increased prevalence of ADHD in highly dentally anxious adults and the need to pay special attention to these patients because of greater treatment needs and increased dental anxiety.