Sibling bullying is associated with various psychosocial difficulties. We investigated this in 231 individuals with Autism Spectrum Disorder (ASD) and 8180 without ASD between middle childhood (age 11 years) and early adolescence (age 14 years). On the whole, self-reported sibling bullying decreased from middle childhood to early adolescence. Despite this, individuals with ASD continued to report more sibling bullying as both perpetrator and victim in early adolescence than those without ASD. We found that self-report sibling bullying in middle childhood was associated with psychosocial difficulties in early adolescence. Moreover, individuals with ASD were more likely to report being bullied by both siblings and peers in middle childhood and this pattern of victimisation was associated with concurrent and longitudinal psychosocial difficulties.