Purpose – The purpose of this paper is twofold. First to ascertain the efficacy of current police reception screening to detect detainees with intellectual disability (ID). Second to assess the validity of a short targeted screen for ID among police custody detainees. Design/methodology/approach – The study comprised three stages. First, 248 police custody detainees were assessed for a range of health morbidities, including a pragmatic clinical evaluation of ID. For those with suspected ID, the police custody screens were scrutinised for evidence that this had been detected. Second, a new police health screen, incorporating a short screen for ID, was piloted. Totally, 351 detainees were assessed in the same way as in part 1 with the new screens being scrutinised for evidence that ID had been detected where relevant. Third, the new police screen for ID was validated among a sample of 64 inpatients, some with ID and some without, from forensic inpatient services. Parts 1 and 2 were carried out in the Metropolitan Police Service, London. Part 3 took place in one NHS Trust. Findings – In parts 1 and 2, the rate of detainees with suspected ID was 2-3 per cent. The standard police screen detected 25 per cent of these detainees in part 1. When the new screen was introduced in part 2, the sensitivity for ID increased to 83 per cent. However, there was no requisite improvement in the proportion of detainees with ID receiving an Appropriate Adult. In the inpatient study, the new screen showed a good level of sensitivity (91 per cent) and reasonable specificity (63 per cent). Practical implications – It is possible to improve the detection rate of detainees with suspected ID by introducing a short ID screen into the police custody officers’ reception health screen. Originality/value – The Health Screening of People in Police Custody (HELP-PC) study is a project evaluating screening for health morbidity among police custody detainees. Other data from this study have been reported elsewhere, but this is the first time the data pertaining to ID screening has been reported in detail.