Background: The aim of this study was to investigate the demographic, clinical characteristics, and service systems of patients with autism spectrum disorder (ASD) and/or intellectual disability presenting to a large paediatric hospital emergency department (ED) with behaviours of concern (BOC) over a two-year period. Method: Retrospective audit of ED presentations with BOC in patients with ASD and/or intellectual disability from 1 January 2019 to 31 December 2020, at the Royal Children's Hospital, Melbourne, Australia. Results: There were 124 presentations (84 patients) in 2019 and 129 presentations (82 patients) in 2020. The mean age was 11.7 years. 55% arrived by ambulance, 24% required physical restraint, and 26% required sedation. Re-presentation was predicted by single-parent household, child protection involvement, and requirement of an interpreter. Conclusions: Children and adolescents with ASD and/or intellectual disability regularly present to ED with BOC. New models of care are required to better support this highly vulnerable patient group.