Background: Limited data exist on problematic sexual behaviour (PSB) in youth with developmental disabilities in South Korea. Method: Sixty-one parents of children with intellectual disabilities or autism spectrum disorder (aged 13-30) reported children's PSB and emotional, behavioural, cognitive, and interpersonal factors. The frequency of PSB in children with developmental disabilities was verified, and various factors' effects on PSB were examined through multiple linear regression analysis. Results: There were no significant differences in PSB levels between children based on sex and age group. The externalising tendency and a history of family conflict predicted higher PSB. In contrast, protective factors had no significant predictive effects. Conclusions: PSB may vary depending on emotional and interpersonal factors, as well as cognitive deficits. Our findings emphasise the importance of interventions for PSB that consider both intrapersonal and interpersonal aspects.