Autistic children experience high rates of mental health challenges, and links have been found between child mental health and the parent-child relationship. As parents of autistic children are often actively involved in their child's treatment, it is important to consider aspects of the parent-child relationship within this context. The present study investigated changes in a component of the parent-child relationship, the coherence of parental representations, following participation in a 10-week cognitive behavioural therapy intervention designed to address autistic children's mental health challenges. Relationships were examined between coherence and child characteristics (i.e., autism symptoms, mental health), and associations with child treatment outcomes (i.e., mental health). Participants included 81 children (89% boys) aged 8 to 13 years and their parents (85% mothers) aged 35 to 54 years. Baseline levels of coherence were related to children's mental health symptoms but not autism symptoms. Although there were no significant changes in overall coherence across therapy, subscale-level improvements (i.e., concern, acceptance) emerged. Changes in coherence across therapy were linked with children's post-intervention behavioural symptoms and were approaching significance for internalizing problems, but were not associated with externalizing problems. It is critical to investigate factors that shape the coherence of parents' representations of their children, as this may provide insight into potential targets for intervention. Ascertaining whether participation in therapy improves parental coherence, and consequently child treatment outcomes, can advocate for parent-involved therapy, which will ultimately benefit the well-being of autistic children.