This study documents the relation between an autism spectrum disorder (ASD) diagnosis, increases in intervention, and changes in parent-child interaction quality. Information about intervention and observations of interaction were collected before diagnosis and a half year after diagnosis for 79 low-risk toddlers who had screened positive for ASD risk during a well-baby checkup. Children diagnosed with ASD (n = 44) were 2.69 times more likely to increase intervention hours. After ASD diagnosis, the relation between intervention and interaction quality was complex: although increases in intervention and interaction quality were only modestly related, the overall amount of intervention after diagnosis was associated with higher quality interactions. Moreover, lower quality interactions before diagnosis significantly increased the likelihood that intervention would increase post-diagnosis.