Many children with autism spectrum disorder (ASD) have problem behaviors that interfere with learning and social interaction. This randomized controlled trial compared treatment with functional communication training (FCT) to "treatment as usual" for young children with ASD (n=38, ages 21-84 months). FCT was conducted by parents with training and real-time coaching provided by behavioral consultants using telehealth. FCT treatment via telehealth achieved a mean reduction in problem behavior of 98% compared to limited behavioral improvement in children receiving "treatment as usual" during a 12-week period. Social communication and task completion also improved. For children with ASD and moderate to severe behavior problems, parent-implemented FCT using telehealth significantly reduced problem behavior while ongoing interventions typically did not.