Purpose: A comparison of parents' experiences of getting a diagnosis for their child with autism, attention deficit hyperactivity disorder (ADHD) and both diagnoses can inform our understanding of common and unique themes across these neurodevelopmental conditions. Method: A quantitative and qualitative online anonymous survey of 288 New Zealand parents of children diagnosed with autism (n = 111), ADHD (n = 93), or both conditions (n = 84) was conducted. Open-ended questions were analysed using reflexive thematic analysis. Results: Parents described an adversarial diagnosis and support system where seemingly arbitrary criteria and thresholds were applied. Key themes specific to the different diagnostic groups were also identified. Conclusions: Common themes of parents' experience across the different neurodevelopmental conditions highlight the need for changes to the diagnostic process.