Patients with undiagnosed or rare diseases often remain without a diagnosis for many years. Many are misdiagnosed or treated symptomatically without having an identified underlying disease process. Health care providers in general practice and subspecialists are equipped to diagnose diseases commonly seen. Most practitioners are unlikely to be familiar with uncommon manifestations of a common disorder and have little or no experience with rare diseases. Multidisciplinary teams are effective in reviewing patients with undiagnosed and rare diseases and in developing a new diagnostic strategy for appropriate evaluation. A medical librarian and an access coordinating navigator are essential members of the team.