Autistic adults experience significant unmet healthcare needs, with opportunities for improvement in both the systems and the practitioners who serve this population. Primary care physicians/practitioners (PCPs) are a natural choice to provide comprehensive care to autistic adults but often lack experience in serving this population. This pilot study developed and tested an Extension for Community Healthcare Outcomes (ECHO) Autism model adapted from our previous work, focused specifically on training PCPs in best-practice care for autistic adults. The project was informed directly by the perspectives and preferences of autistic adults, caregivers, and PCPs. Two consecutive cohorts of PCPs participated in ECHO Autism Adult Healthcare sessions. Each cohort met 1 h twice a month for 6 months, with 37 PCPs (n = 20 in Cohort 1, and n = 17 in Cohort 2) participating. Based on findings from the first cohort, adjustments were made to refine the session preparation, curriculum, conduct of the ECHO, resources, and evaluation. After participation in the ECHO Autism program, PCP self-efficacy and satisfaction improved, while the number of perceived barriers did not change. Knowledge did not improve significantly in Cohort 1, but after adjustments to the training model, participants in Cohort 2 showed significant knowledge gains. While attention to systems of care is critical to addressing barriers in healthcare in the autistic population, the ECHO Autism Adult Healthcare model is feasible and holds promise for improving PCP satisfaction and self-efficacy in working with autistic adults.