The Telethon “Undiagnosed Diseases” program focuses on severe rare pediatric diseas using a multidisciplinary approach. It addresses cases with negative results from multiple standard tests, assessing the need for advanced genomic analyses, such as Trio WGS, long-read sequencing, methylation, Optical Mapping and RNASeq. So far, 1,336 diagnoses have been made in 989 families. The program helps reduce the diagnostic odyssey typical of rare genetic diseases, enabling early, accurate diagnoses, the discovery of new disease genes, and targeted therapies.