In the wake of dramatic increases in autism spectrum disorder (ASD) diagnosed in children we now see an unprecedented increase in diagnosed persons with ASD entering adolescence and young adulthood. The research base focusing on autistic adolescents and adults to inform practice, however, is relatively underdeveloped. The symposium draws on different research efforts across the EU and addresses important areas regarding long term outcome, including intervention outcome; factors affecting outcome; phenotypic measures; and services delivery characteristics for autistic adolescents and adults.