Seeking an adult assessment for co-occurring Autism and ADHD in Australia can feel like navigating a system that was not designed with you in mind. Most assessment pathways were built around childhood presentations, and the adults who arrive at their GP's office in their 20s, 30s, or 40s — often after years of unexplained struggles — face a landscape of conflicting referral advice, long waiting lists, and significant out-of-pocket costs. This guide maps the realistic path from first conversation to formal diagnosis.
The first practical step is a GP appointment to discuss your concerns and request a referral. A general practitioner cannot diagnose Autism or ADHD directly, but they can refer you to a psychiatrist or registered psychologist under Medicare's Better Access Initiative, which provides subsidised sessions. It is worth being specific in this appointment: bring a written summary of your experiences across different life domains — school history, work history, relationships, sensory sensitivities, attention patterns — because GPs who see you briefly may underestimate the complexity of what you are describing. Ask for referrals to both a psychiatrist and a psychologist if a comprehensive dual assessment is your goal.
The professionals involved in adult assessment vary in what they can diagnose and prescribe. Psychiatrists are medical doctors who can diagnose both conditions, prescribe ADHD medication directly, and assess for co-occurring mental health conditions that may complicate the presentation. Registered psychologists with specialist experience can assess and diagnose both conditions but cannot prescribe — they will refer to a psychiatrist or GP for any medication component. Paediatricians assess children and adolescents, not adults. For a dual AuDHD assessment, many clinicians recommend a psychologist-led assessment followed by a psychiatric review for the medication question, which can reduce the total cost compared to a full psychiatric evaluation for both conditions.
For the actual assessment appointments, preparation significantly affects the quality of the outcome. Bring school reports, old report cards, and any relevant childhood records if you can access them — clinicians look for evidence that traits were present before age 12. Ask a parent, sibling, or close friend to provide a collateral history if you are comfortable doing so, as retrospective self-report can miss things that people who knew you as a child will remember clearly. Write down specific examples rather than generalities: 'I have missed three rent payments because I forgot' is more useful to a clinician than 'I struggle with executive function.'
The case for pursuing both assessments simultaneously rather than sequentially is well-supported by clinical experience in this population. ADHD and Autism share overlapping traits — both can produce inattention, difficulty with social communication, and sensory sensitivities — which means that assessing for one in isolation can produce a skewed picture. A clinician who finds ADHD first may attribute everything to it and miss the autistic profile; one who finds Autism first may conclude that what looks like inattention is actually an autistic processing style rather than a co-occurring attention disorder. Dual assessment allows the clinician to weight the interaction of both conditions, which typically produces a more accurate and useful clinical picture.