Background: During adolescence, risk and opportunity are both elevated. Adolescents with autism spectrum disorder (ASD) and ASD with co-occurring intellectual disability (ASD+ID) must navigate this period of psychological and physical developmental changes with at least one neurodevelopmental disorder. For children with these neurodevelopmental disorders, adolescence is associated with an increased risk of the onset of mental health conditions and excessive weight gain. For children without neurodevelopmental disorders, higher levels of physical activity are associated with improved mental and physical health, and a predominantly sedentary lifestyle is associated with poor health-related quality of life. However, these relationships have been relatively unexplored for children with neurodevelopmental disorders. The aim of this study was therefore to explore the relationships between psychological wellbeing and physical factors (physical health and physical activity) for adolescents with ASD and ASD+ID. Methods: Participants were primary caregivers of 38 adolescents aged 12 – 19 years of whom 23 had a diagnosis of ASD and 15 had a diagnosis of ASD+ID. Data were collected through an online survey. Measures focused upon psychological wellbeing (mental health and health-related quality of life) and physical factors (BMI, waist-to-height ratio, and physical activity levels). Results: Few relationships were found between the psychological wellbeing and physical factors. For the total sample, higher levels of physical activity at school were related to poorer mood. When split by diagnostic subgroup, higher physical activity at school was related to higher uncertainty for the ASD+ID subgroup only. Discussion: The results of this study add to limited literature around wellbeing and physical activity research for adolescents with ASD and ASD+ID. Differences were found between adolescents with ASD and ASD+ID, highlighting the need for diagnostic specific research. The relationships between physical activity at school and mental health warrant further investigation to see if there may be any wellbeing benefit in physical activity for adolescents with ASD, and especially for those with ASD+ID who need mental health support alternatives to cognitive psychotherapy.