Objectives: Findings about the psychological adjustment of siblings of children with autism spectrum disorder have been inconsistent in western literature and little is known among non-western societies. This study explored the psychological adjustment of siblings of children with autism spectrum disorder in Hong Kong. Methods: A total of 116 families with siblings of children with autism spectrum disorders co-morbid with learning disability were included in the study. Parents completed questionnaires about sibling emotional and behavioural adjustment, and their own mental well-being, quality of life, and family functioning. Siblings completed a questionnaire on their relationship with the autistic proband. Results: Parent ratings did not reveal any significant negative impact on the emotional and behavioural adjustment of the typically developing siblings of children with autism spectrum disorder, but there were concerns about their peer relationships and weak prosocial behaviours. When cut-off scores were used to screen for risk of mental health problems, a quarter of the siblings warranted further assessment. Parents’ quality of life and family functioning were significant predictors of sibling adjustment. Conclusions: In managing children with autism spectrum disorder, it is necessary to bear in mind the adjustment of their siblings, especially their peer relationships and prosocial behaviour. Adopting a holistic approach to address the psychosocial needs of the parents can facilitate sibling adjustment.