Despite the large number of people with intellectual disabilities (ID) and the fact they are more likely to be victims and witnesses of crime, only two published studies have investigated their performance on identification line-up parades. In the present study we examined the identification performance of adults with and without ID on both a perpetrator-present and a perpetrator-absent photographic line-up. In addition, we investigated factors that could explain any potential difficulties with identification performance, such as face recognition performance (as measured by a standardised test), eyewitness confidence, understanding of the purpose of a line-up, and memory for non-biased line-up instructions. In comparison with typical adults, participants with ID demonstrated poorer performance across both perpetrator-present and perpetrator-absent photographic line-ups, yet were more confident in the accuracy of their responses. In addition they had poorer face recognition performance, were less likely to understand the purpose of the line-up, and were less likely to remember the non-biased line-up instructions. This pattern of difficulties is discussed in relation to the development of future research and interventions. (Contains 1 table.)