Background: The clinical diagnosis of ADHD is time-consuming and error-prone. Secondary care referral results in long waiting times, but primary care staff may not provide reliable diagnoses. The Development And Well-Being Assessment (DAWBA) is a standardised assessment for common child mental health problems, including attention deficit/hyperactivity disorder (ADHD), which can be rapidly scored by skilled specialist clinicians, who may be remote from the interview, thus avoiding referral. Method: A representative clinic sample of routine cases suspected of ADHD underwent an assessment which included the DAWBA alongside a confirmatory assessment with a skilled clinician. Another clinician provided DAWBA-based diagnoses blind to the clinic view. Bayesian statistical modelling was used to include clinic diagnostic uncertainty in the analyses. Results: Eighty-four cases were assessed. For ADHD, the predictive value of a positive or negative DAWBA diagnosis was greater than 0.8, with negligible bias. Non-hyperkinetic behaviour disorders had higher, emotional and autistic disorders lower predictive values, though all greater than 0.75: there was, however, evidence of bias. Conclusions: Diagnoses of ADHD based on senior clinician review of the DAWBA completed by parents, teachers and young people aged 11 plus may be sufficiently accurate to permit clinical diagnosis without direct patient contact by the diagnosing clinician. This could improve access to accurate diagnoses of ADHD in primary care while freeing up senior clinicians to focus on complex and refractory cases in secondary care.