While self-injurious behaviors (SIB) can cause significant morbidity for children with autism spectrum disorders (ASD), little is known about its associated risk factors. We assessed 7 factors that may influence self-injury in a large cohort of children with ASD: (a) atypical sensory processing; (b) impaired cognitive ability; (c) abnormal functional communication; (d) abnormal social functioning; (e) age; (f) the need for sameness; (g) rituals and compulsions. Half (52.3%, n = 126) of the children (n = 241, aged 2-19 years) demonstrated SIB. Abnormal sensory processing was the strongest single predictor of self-injury followed by sameness, impaired cognitive ability and social functioning. Since atypical sensory processing and sameness have a greater relative impact on SIB, treatment approaches that focus on these factors may be beneficial in reducing self-harm in children with ASD.