Aim: The aim of this study was to study systematically social, communication, and repetitive/restrictive (SCRR) behavioural difficulties and clinical autism spectrum disorder (ASD) in children with optic nerve hypoplasia (ONH) and/or septo-optic dysplasia (SOD), and to investigate the relationship between visual impairment, SCRR difficulties, ASD, and cognition. Method: A case-note study of clinic records from a specialist developmental vision service was completed. Standardized assessments of vision and development and clinician judgements about SCRR difficulties and clinical ASD were made by a multidisciplinary team. Results: A total of 45 females and 38 males (mean age 3y 5mo; range 10mo-6y 10mo) with ONH or SOD and profound visual impairment (PVI) or severe visual impairment (SVI) were assessed. A total of 58% of children had at least one SCRR difficulty, and 31% had a clinical diagnosis of ASD. The prevalence of ASD was slightly higher in children with SOD than in children with ONH (36% vs 26%) also slightly more frequent in children with PVI than in children with SVI (36% vs 27%). The prevalence of SCRR difficulties was statistically higher in children with PVI than in children with SVI (p=0.003). Clinical ASD was most likely to be diagnosed between 2 years 4 months and 4 years 6 months. Development was significantly delayed in children with ASD compared with children without social communication difficulties (p=0.001). Interpretation: Children with SVI or PVI are at risk of SCRR difficulties and clinical ASD. Children with ONH and/or SOD and visual impairment have a similar risk of developing clinical ASD as other visual impairment groups. However, ASD prevalence data from this study are a minimum estimate, as some young children may have developed ASD behaviours in later childhood. Developmental surveillance for children with ONH and/or SOD should continue until at least the age of 4 years 6 months.