BackgroundLittle is known about how clinical features prospectively influence peer relationships in autistic populations. AimsThis study investigated the clinical symptoms mediating the link between autism spectrum disorder (ASD) diagnosis and peer relationships at follow-up, i.e. the second time evaluation of this study. MethodsThe sample consisted of 366 autistic youths and 134 non-autistic comparisons. The autistic traits and emotional/behavioral problems were measured at baseline by Social Responsiveness Scale (SRS) and Child Behavior Checklist (CBCL). The interactions and problems with peers were assessed by the Social Adjustment Inventory for Children and Adolescents (SAICA) at follow-up. ResultsEach subscore of SRS and CBCL showed significant mediation effects. Multiple mediation analyses showed atypical social communication, social awareness problems, and delinquent behaviors mediated the link from ASD to less active peer interactions after controlling for sex, age, and IQ. Moreover, atypical social communication, social-emotional problems, and attention difficulties predicted problems with peers. After considering these mediation effects, the diagnosis of ASD still demonstrated a significantly direct effect on peer relationships at follow-up. Conclusions and implicationsOur findings support that social-related autistic features, attention problems, and delinquent behaviors mediated a link between ASD and peer relationships. These mediators are potential measures for improving interactions and decreasing difficulties with peers in the autistic population.