Elevated parenting stress among parents of children with autism spectrum disorder is well-documented; however, there is limited information about variability in parenting stress and relationships with parent ratings of child functioning. The aim of this study was to explore profiles of parenting stress among 100 parents of young children with autism spectrum disorder enrolled in two clinical trials and potential relationships between parenting stress and parent ratings of child functioning at the baseline timepoint. Secondary aims examined differential patterns of association between parenting stress profiles and parent versus clinician ratings of child functioning. A "k"-means cluster analysis yielded three different profiles of parenting stress (normal, elevated, and clinically significant) using scores on the Parenting Stress Index--Short Form. One-way analyses of variance revealed differential patterns of parent ratings across the three parenting stress profiles on certain domains of child functioning (e.g. problem behaviors and social impairment) and family empowerment, but similar ratings of child receptive and expressive language abilities. Clinicians blinded to study conditions also rated child functioning, but clinician ratings did not differ by parenting stress profile. Findings emphasize the importance of identifying parenting stress profiles and understanding their relationship with parent ratings, with implications for interpreting parent-report measures and measuring child response in treatment trials.