The third edition of the Agency for Healthcare Research and Quality's landmark federal publication, "Registries for Evaluating Patient Outcomes: A User's Guide," will include 34 new case examples, 11 new chapters, and for the first time, patient representative contributions. Chapter 20, aptly named "Rare Disease Registries" and reviewed by Quintiles, discusses the increasing interest in using registries to study rare diseases and reviews the unique challenges in enrollment of patients, data collection, retention and analysis and interpretation.