This document discusses research on why youth mentoring relationships end. It finds that about half of formal mentoring relationships last less than a few months. Relationship failures can potentially harm youth. The document examines factors related to youth, mentors, the relationship process, and programs that may contribute to early relationship endings, such as lack of training, expectations, cultural differences, and program support. Preventing relationship failures requires screening mentors, setting clear expectations, providing ongoing support and training, and discussing closure from the start of the match.