Abstract Early and intensive intervention (EI) for children with autism spectrum disorder (ASD) is considered to beBbest practice^to reduce the symptoms of autism andmaximize the outcome for children’s functioning. Many studies have established the effectiveness of, particularly, early intensive behavioral intervention, and in some cases improvements have been impressive, with children moving off the autism spectrum. However, very few long-term follow-up studies have been conducted to determine if the progress seen as a result of EI has been maintained as children with ASD con-tinue through school. Eight long-term follow-up studies pub-lished between 1993 and 2014 are reviewed. The researchers reported that although most children had made progress in many areas as measured by standardized assessments, chil-dren in some studies had regressed. Significant difficulties in autism symptomatology, behavior, and social skills remained at follow-up for many children across studies. It appears that ongoing, uninterrupted intervention after the conclusion of early intervention is necessary to ensure gains made in EI are maintained. However, because of numerous methodolog-ical issues in the studies, these conclusions cannot be defini-tive, and additional longitudinal research is called for. Keywords Autism spectrum disorder.Early intervention. Follow-up. Primary school. Developmental disorders