The EuRRECa project, launched in 2018, includes the EuRRECa Core Registry which has been operational since June 2019 and is approved by the Science Committee of Internal Medicine at the Leiden University Medical Center, the Netherlands and the National Ethics Service and Information Governance authorities in the UK. The information collected by the Core Registry is what is expected to be collected during routine clinical care and may be shared with approved users to perform or develop new research studies. The Core Registry does not collect any information on names, addresses and local hospital numbers. Patients can also access their own information in the Core Registry. All information is kept strictly confidential and handled through secure password protected electronic systems and only those who are directly involved with the Registry are able to obtain access. The reported data are stored on a secure server in the Leiden University Medical Center and all information provided is kept in compliance with the General Data Protection Regulation (GDPR 2016/679).