Objective: This study determined whether child and family environment factors are associated with differences in developmental trajectories of emotional and behavioral dysregulation in children with autism spectrum disorder (ASD).Method: Participants included 186 families of a child with ASD (5-12 years old at baseline; 86% male; 83% non-Hispanic Caucasian; 35% comorbid intellectual disability). At each of the four time points (each spaced 12 months apart), mothers and fathers within each family completed well-validated measures on their own mental health, their child's dysregulation, their parent-child relationship, and their parent couple relationship. Longitudinal multi-level modeling was used to describe trajectories of dysregulation across 3 years and test whether parent depression, closeness in the parent-child relationship, and positive parent dyadic coping were associated with differences in child trajectories.Results: On average, child dysregulation decreased across time. Closer mother-child and father-child relationship quality was associated with lower baseline dysregulation. More severe child restricted and repetitive behaviors, fewer maternal depression symptoms, and more positive parent dyadic coping were associated with declines in child dysregulation over time.Conclusions: On average, children with ASD become less dysregulated across time. However, there is important variability in dysregulation trajectories of children with ASD. Children with ASD who have a high (versus low) severity of restricted and repetitive behaviors appear to be at risk for greater dysregulation. The family environment, and specifically a closer parent-child relationship, better maternal mental health, and more positive couple coping, may contribute to a pattern of improved child regulation across time in ASD.