Autism Spectrum Disorder (ASD) is associated with social skills deficits and co-occurring mental health difficulties. ASD frequently co-occurs with Intellectual Disability (ID). There is scant literature exploring the association between social skills and mental health in children with ASD, with or without ID. Participants were 292 children aged six to 13 with ASD (217 without ID; 76 with Mild ID). Parents and teachers rated social skills and mental health using standardised questionnaires. Greater mental health difficulties were associated with greater social responsiveness difficulties and poorer social skills across the sample. Effect sizes were large. Social skills explained a significant proportion of the variance in mental health scores across the sample. The study has important implications for treatment and future research.