Young children with autism spectrum disorder can benefit from early detection and intervention to moderate autism spectrum disorder's effect on their development. Routine screening with standardized instruments facilitates early identification. However, many screen-positive children do not receive referrals for evaluation, complete diagnostic evaluations, or engage in services. This is especially true for children of color and those from less educated or low-income families. The Screening and Linkage to Services for Autism trial evaluated the effect of family navigation on referral and evaluation for autism spectrum disorder in screen-positive toddlers. The trial was conducted in an urban, low-income population. It was designed to test "real-world" implementation of family navigation. We randomly assigned 275 children aged 16-30 months with an initial positive autism spectrum disorder screen to receive navigation if indicated or usual care. Navigation increased the number of at-risk toddlers who were evaluated for autism spectrum disorder. It also improved the quality of autism spectrum disorder screening in primary care clinics. However, many children failed to receive indicated referrals for evaluation. Navigation did not improve referral rates. Furthermore, nearly half of families who were potentially eligible for navigation could not be contacted. Other ways of structuring the navigation program may be necessary to improve families' access to and acceptance of navigation, especially in the setting of financial, cultural, and linguistic barriers. Our trial nevertheless showed that family navigation may be an important tool for reducing systemic inequalities in the early identification and treatment of young children with autism spectrum disorder.