Background It is crucial that children and young people and adults with a learning disability are identified in a timely manner so that they can access appropriate support and interventions. However, it is often challenging to identify learning disability in autistic people, although it is common among this population.

Aim To examine the sensitivity (accuracy) and test-retest reliability of the online version of the Child and Adolescent Intellectual Disability Screening Questionnaire (CAIDS-Q) in identifying learning disability in people who are autistic and in those who are not autistic.

Method Anonymous CAIDS-Q data were used from 1,203 people who had completed the tool about a child or young person. Of these children and young people, 396 were reported to be autistic and 807 were not reported to be autistic. To determine the tool’s sensitivity, the outcome based on the CAIDS-Q was compared with whether or not the person was reported to have a learning disability by the user of the tool. To determine the tool’s test-retest reliability, data were analysed from a subsample of 139 people who had completed the screening tool about the same child or young person on two occasions within one week.

Results This study found that the online version of the CAIDS-Q accurately identified those with reported learning disability in 92% of those who were autistic and in 83% of those who were not autistic. The study also found that the CAIDS-Q scores were stable over a short period of time.

Conclusion The results suggest that the online CAIDS-Q can be used to help identify learning disability in people who are autistic and in those who are not autistic, indicating that the tool could be used in clinical practice to recognise those who may benefit from additional assessment, interventions and support.