Abstract Background Autism Spectrum Disorder (ASD) is a developmental disorder characterized by deficits in social interaction/communication, restricted interests and repetitive behaviours. Recent discussions have emerged worldwide regarding a possible “overly-inclusive” diagnosis of ASD, adding heterogeneity around presentation/etiology and comorbidities. Objectives This study aimed to determine the frequency and characteristics of comorbidities among children diagnosed with ASD in Manitoba, and to evaluate differences in presentation between those with and without medical comorbidities. As comorbid neurodevelopmental disorders such as global developmental delay (GDD) and attention-deficit yyperactivity disorder (ADHD) are common in children with ASD, these were not included as “medical comorbidities” and were studied separately. Design/Methods We conducted a retrospective chart review of >2000 electronic charts at the main referral site for children <6 years requiring evaluation for ASD in Manitoba. All children aged 0-5 years diagnosed with ASD at this site between May 2016 to September 2021 were identified. X2 and t test were used to compare groups. Results Of the total of 1858 children identified, 1459 (78%) were male, 252 (13.5%) were born prematurely, 504 (27%) had ≥1 medical comorbidity. Most common medical comorbidities were neurological (12.7%) and allergies/eczema (6.1%). Comorbid GDD was diagnosed in 428 (23%). Age of referral to RCC and age of diagnosis did not differ between groups. Medical comorbidities were more common among preterm children (31% vs. 26%, p:<0.01) and children with comorbid GDD (35% vs. 18.6%, p:<0.01). There was no significant difference in overall presence of medical comorbidities by sex (29.5% vs. 26.6%, p: 0.25); however, girls had a statistically significant higher incidence of neurological comorbidities, e.g. cerebral palsy, epilepsy, hypotonia NYD (16% vs. 12%, p:0.03). Conclusion Results of this study are consistent with previous studies, which note high comorbidity rates among children with ASD. The high rates of associated neurological conditions, GDD, and prematurity add heterogeneity to this group and may relate to the reported “overly-inclusive” diagnosis. This study will be used as a catalyst for guiding further prospective studies in the area.