The paediatric-adult split in mental health care necessitates young people to make a transition between services when they reach the upper end of child and adolescent mental health services (CAMHS). However, we know that this transition is often poor, and not all young people who require ongoing support are able to continue care in adult mental health services (AMHS). These young people are said to have fallen through the gap between services. This research aimed to explore the reasons why young people fall through the gap between CAMHS and AMHS, and what effect this has had on them and their families. Narrative interviews were conducted with 15 young people and 15 parents, representing 19 unique transition stories. Themes were identified collaboratively using thematic analysis. Reasons for falling through the gap were grouped into systemic problems and problems with the quality of care received. Effects of falling through the gap were grouped into separate themes for young people (feeling abandoned; struggling to manage without continued care; problems with medication) and parents (emotional impact of care ending; parents taking an active role in the young person’s care). To our knowledge, this is the first qualitative study that has focused only on the experiences of young people who have fallen through the gap between services. This research adds novel findings to existing literature regarding barriers to transition and the effects of discontinuity of care.