Although several notable collections of fan fiction exist in libraries, such as the Sandy Hereld Fanzine Collection at Texas A&M University (http://oaktrust.library.tamu.edu/handle/1969.1/149935) and the digital fanzine archives at the University of Iowa (http://www.lib.uiowa.edu/sc/resources/fandomresources/), not much attention is given to the systematic selection, acquisition, indexing, preservation, and sharing of fan works in the UK, considering the popularity of fandom, the volume of creative work that exists, and the rate at which new texts are produced. Here we present the results of an investigation into the extent to which UK libraries collect and manage fan fiction, and our attempts to ascertain the reasons underlying collection policy in local, public, special, academic, and national institutions. Our report is based on a review of recent literature, an analysis of the collection policies of a selection of UK libraries, and a brief survey of the views of Library & Information Science students. The empirical work was carried out in spring 2016. Results show that there is a little-known and less-understood dark side to fan fiction, in regard to how it is understood and valued in the library sector, which feeds a widening gap in our cultural heritage.