Behavior problems in children with autism spectrum disorder (ASD) may exacerbate parenting stress. Parenting self-efficacy and family resources may influence this association. We examined cross-sectional statistical mediation effects of parenting self-efficacy on the relationship between child behavior problems and parenting stress and hypothesized that family-level resources moderated this indirect effect. Participants included 132 underserved (Medicaid-eligible) children with ASD (ages 3-13) with racial/ethnic diversity; many (63%) had intellectual disability. Greater externalizing problems were linked with lower parenting self-efficacy, which in turn was associated with increased parenting stress. A larger mediation effect was observed for families with fewer resources. A plausible alternative model (parenting stress mediating parenting self-efficacy) exhibited poorer fit. Implications for family supports and benefits of longitudinal follow-up are discussed.