Background : Social skills interventions are commonly deployed for adolescents with autism spectrum disorder (ASD). Because effective and appropriate social skills are determined by cultural factors that differ throughout the world, the effectiveness of these interventions relies on a good cultural fit. Therefore, the ACCEPT study examines the effectiveness of the Dutch Program for the Education and Enrichment of Relational Skills (PEERS®) social skills intervention. Methods/design : This study is a two-arm parallel group randomized controlled trial (RCT) in which adolescents are randomly assigned (after baseline assessment) to one of two group interventions (PEERS® vs. active control condition). In total, 150 adolescents are to be included, with multi-informant involvement of their parents and teachers. The ACCEPT study uses an active control condition (puberty psychoeducation group training, focussing on social-emotional development) and explores possible moderators and mediators in improving social skills. The primary outcome measure is the Contextual Assessment of Social Skills (CASS). The CASS assesses social skills performance in a face to face social interaction with an unfamiliar, typically developing peer, making this a valuable instrument to assess the social conversational skills targeted in PEERS®. In addition, to obtain a complete picture of social skills, self-, parent- and teacher-reported social skills are assessed using the Social Skills improvement System (SSiS-RS) and Social Responsiveness Scale (SRS-2). Secondary outcome measures (i.e. explorative mediators) include social knowledge, social cognition, social anxiety, social contacts and feelings of parenting competency of caregivers. Moreover, demographic and diagnostic measures are assessed as potential moderators of treatment effectiveness. Assessments of adolescents, parents, and teachers take place at baseline (week 0), intermediate (week 7), post intervention (week 14), and at follow-up (week 28). Conclusion : This is the first RCT on ...