Youth with autism spectrum disorder (ASD) face challenges accessing needed services as they transition to adulthood. Correlates of service access identified in the literature—such as family resources, race/ethnicity, or youth functioning—can be difficult to change and may not be feasible targets for intervention. This study focused on a potential contributor to service access that is malleable: parental advocacy. Specifically, we examined the association between parental advocacy activities and number of services among transition-aged youth with ASD, after accounting for indicators of youth functioning and family demographic variables (high school exit, co-occurring intellectual disability, social impairments, adaptive behaviors, race/ethnicity, state of residence, family income, and parental depression). Participants included 185 families of youth with ASD who are part of an ongoing randomized controlled trial. Data were collected at baseline (prior to intervention) via parental questionnaire and structured interview. Using hierarchical regression analyses, we found that parental advocacy activities were significantly and strongly associated with service receipt after controlling for youth functioning and family demographic factors. Youth whose parents are less involved in advocacy activities might be at-risk for service disparities. To close the gaps for service disparities, future interventions may target parental advocacy skills. Lay abstract It can be difficult for youth on the autism spectrum to get the services they need after they leave high school. Because of this, many studies have examined the different factors that are related to service access. These studies have shown that youth on the autism spectrum who belong to an underrepresented racial or ethnic group or whose families have lower incomes are less likely to receive the services that they need. However, it is difficult or impossible to change things like race/ethnicity or family income. It is important to also identify factors that might improve service access that we can change. One potential factor that fits into this category is parental advocacy activities. Using data collected from 185 parents of youth on the autism spectrum, we found that more parental advocacy activities were related to youth receiving more services, even after accounting for variables related to the functioning of the youth (e.g. whether they have an intellectual disability, their autism symptom severity) and demographic information about the family (e.g. state in which they live, parental race/ethnicity, and family income). Our findings suggest that building parental advocacy skills may be one important way to increase the number of services that youth on the autism spectrum receive as they transition to adulthood.