OBJECTIVES: Patient registries are important tools for health care research.  The goal of this project, sponsored by the Agency for Healthcare Research and Quality (AHRQ), is to design and implement the Registry of Patient Registries (RoPR), the first searchable, public database designed specifically to provide information about registries.  The RoPR is integrated with ClinicalTrials.gov, supports research collaboration, reduces redundancy, and improves transparency in observational clinical research. METHODS: The RoPR consists of a registration system and a public search Web site.  The registration system collects over forty data elements which define a registry profile.  The search site serves as a central listing of registries and includes options to filter for relevant profiles.  RoPR registration is integrated with ClinicalTrials.gov: users registering a study on ClinicalTrials.gov who designate it as a patient registry are presented with a pop-up window displaying the RoPR registration system.  Users complete and submit the requested data elements, creating a registry profile in the RoPR that is linked to the ClinicalTrials.gov listing through a unique identifier, the NCT ID.   RESULTS: The RoPR was launched on December 1, 2012.  As of January 11, 2013, 54 new patient registries are registered on ClinicalTrials.gov.  Twelve of these have been fully published in the RoPR, representing 21 different condition areas.  Most are classified as disease/disorder/condition (67%), drug (33%), and/or procedure (33%) registries.  Reported registry purposes include effectiveness (50%), safety or harm (42%), natural history of disease (42%) and clinical practice assessment (33%).  A total of 67% of registry sponsors are open to being contacted for collaboration, data access, investigator or patient participation, or for information requests. CONCLUSIONS: The RoPR is a searchable Web site used by registry sponsors to publish information about registries and by members of the public to search for information about existing registries.  Integration with ClinicialTrials.gov presents a user-friendly interface to encourage registration.