ABSTRACTChildren and young people with intellectual disabilities are more likely to experience emotional, behavioural, or mental health difficulties, including a combination of these health problems. There are risks that existing interventions may not be accessible or effective for this group. This program evaluation explored the effectiveness of child-centred play therapy, a developmentally appropriate mental health intervention, for a single group of 42 children with intellectual disabilities aged 4 to 16 years with emotional, behavioural, or mental health difficulties. The intervention was provided by seven therapists trained in the same play therapy protocol and procedures. Parents rated children's emotional and behavioural difficulties before and after play therapy using the Strengths and Difficulties Questionnaire. Statistically significant improvement to children's prosocial skills, emotional and behavioural difficulties, and the impact of these difficulties on everyday life was found at the completion of child-centred play therapy. Children with high-priority referral needs were found to have made greater levels of change. However, with increasing severity of difficulties, children required more time in therapy. A higher level of play therapy training predicted greater prosocial skill development for children and a reduced impact of difficulties on their daily life. This evaluation demonstrated that play therapy may be an effective intervention to use with children with intellectual disabilities and emotional and behavioural difficulties, and warrants further consideration for research and practice by the disability and mental health sectors.