We assessed the clinical utility of the parent-reported Strengths and Difficulties Questionnaire (SDQ) as a screen for emotional and behavioural difficulties in 626 children and young people with intellectual disability. Using the Developmental Behavior Checklist (DBC2-P) to determine clinical caseness, the area under the curve for the SDQ total difficulties score was 0.876 (95% CI 0.841–0.911), indicating that it is a good measure for identifying significant emotional and behavioural difficulties requiring further investigation. Analyses supported the use of the same SDQ cut-off for those with and without intellectual disability, which may assist with consistent and comparable assessment in clinical practice.