Children and youth with Autism Spectrum Disorder (ASD) often present with co-morbid impairments in self-regulation (e.g., difficulty managing their emotions) resulting in unhelpful regulatory approaches such as disruptive compulsive, aggressive and self-injurious behaviour. There is an urgent need to establish novel, precise and effective interventions that promote self-regulation and reduce disruptive behaviours. This project will collect pilot data on the effects of repetitive TMS in reducing disruptive behaviours in youth with ASD, in order to inform the design of a follow-up full-scale clinical trial. Youth with ASD who experience clinically significant difficulties with self-regulation and disruptive behaviour will be recruited. Participants will be randomized to rTMS or sham rTMS for 3 weeks. The overall feasibility of the trial will be assessed. The effect of rTMS on the brain mechanisms of self-regulation and clinical improvement in disruptive behaviours will also be measured. Neurophysiological outcomes, including changes in regional brain network activity for inhibition of behaviour, will be explored.