Improving diagnosis remains a major focus within patient safety. For patients with rare diseases, diagnosis can often be delayed. Established in 2014 and funded by the National Institutes of Health, the Undiagnosed Diseases Network (UDN) applies a multidisciplinary approach to the most challenging diagnostic cases. Over a 20-month period, 601 out of 1519 patient cases were accepted by the UDN for evaluation. The authors report that of the 382 patients who underwent a complete evaluation, a diagnosis was identified in 132 patients.