Objectives <p>The current study evaluated the psychometric properties of the Autism Parenting Stress Index (APSI), a brief measure of caregiver stress specific to autism, in a diverse sample of caregivers with children across a wide age range. Specifically, the study assessed the APSI’s internal consistency, factor structure, test–retest reliability, and convergent validity with the Parenting Stress Index, Fourth Edition (PSI-4).</p> Methods <p>Data were collected from 325 caregivers of children diagnosed with or at-risk for ASD, or who had a sibling with ASD. Participants completed the APSI before and after a summer camp program. A subsample also completed the PSI-4. Analyses include descriptive statistics, subgroup comparisons, Cronbach’s alpha, exploratory factor analysis, test–retest correlations, and correlations with PSI-4 scores.</p> Results <p>Overall, results suggest that the APSI provided adequately reliable scores with this sample of caregivers/children with an internal consistency of 0.87. Exploratory factor analysis supported a three-factor structure: comorbid behaviors, core autism symptoms, and comorbid physical issues. Test–retest reliability over an average of 11&#xa0;weeks was moderate (<i>r</i> = .59, <i>p</i> &lt; .001). APSI Total Scores were significantly correlated with PSI-4 Child, Parent, and Total Stress scores, supporting convergent validity. Additionally, higher APSI scores were associated with male child gender and older age.</p> Conclusion <p>The results of this study, in addition to previous research, provide support for the APSI as a psychometrically robust measure for assessing caregiver stress in families with children with autism and should be leveraged as a tool to improve autism services and future research.</p>