Holocaust denial literature has been treated inconsistently in library collections. At one time Holocaust denial literature was classed and subject headings assigned with Holocaust literature. After specific Library of Congress classification numbers and subject headings for Holocaust denial and Holocaust denial literature became available in the 1990s, works of Holocaust denial and Holocaust denial literature became split in library collections, both in online catalogs and on the shelves. A review of the classification and subject treatment for five well-known works of Holocaust denial was conducted in the Association of Research Libraries (ARL) member catalogs. Collocation of material on the shelves is a popular discovery tool of library users. Works classed together are assumed to be about the same topic. When works of Holocaust denial are classed with works about the Jewish Holocaust, it may inadvertently lend them credibility. Librarians have an ethical duty to reclassify works that have been misidentified in their collections. Most libraries do not collect heavily in this subject area and it would not create an undue burden to reclassify and remark these titles. It would provide a valuable service to the library user. (Contains 9 tables.)