Abstract Background Research registers of potential participants linked to Electronic Health Records (EHRs) provide a basis for screening and identifying people suitable for studies. Such a system relies upon people joining the register and giving permission for their record to be used in this way. This study describes the process of training clinicians to explain EHR-linked research registers to service users, and to recruit them onto the register. Method Training materials were developed for clinicians to help them describe the register to service users. These materials were based upon findings from focus groups reported elsewhere, they were then tested with 31 clinicians in early intervention psychosis services and each clinician discussed the register with service users on their caseload (n = 100 service users). Consultations were recorded and analysed in relation to their coverage of the training criteria. Service users also provided data on the acceptability of the process from their perspective. The content of clinicians’ explanations to service users was described, and then compared against the likelihood of service users joining the register. Interpretive statistics (t-test and Chi-Squared) were used to explore differences between consultations in which service users agreed to join the register, and consultations where they did not agree to join. Results Service users appeared more likely to join the register if they felt control over what they signed up to, this necessitated understanding that they could decide when, how often, and by whom they were contacted, that joining the register did not automatically enlist them to future studies, and that they could change their mind in future. Clinicians’ explanations did not always include that researchers would be able to see the service users’ EHR. Service users often confused the idea of signing up to the register and signing up to studies themselves. Confidentiality was not well explained, but service users were not always concerned by confidentiality. Conclusion EHR-linked research registers provide recruitment opportunities, and help service users to find out about research. Implementing these registers within mental health settings requires a trained clinical workforce and an informed service user population.