As a service to the library community, the Library of Congress adds Dewey Decimal numbers to approximately two-thirds of the books receiving full cataloging at the Library of Congress. This substantially reduces the cataloging effort required by Dewey libraries. However, shelflisting is still a major expense for individual libraries. Copy catalogers frequently modify the call number to meet local needs. Even libraries that accept LC classification without revision may adjust the cutter number to avoid conflicts in their local catalog. Dewey libraries usually add a cutter number or cutter-like addition to the class number and may modify the Dewey Decimal number itself. OCLC and the Library of Congress jointly conducted a study of library cuttering practice to learn the extent and types of changes made to call numbers--particularly cutter numbers--during copy cataloging. The study looked at how both Library of Congress and Dewey Decimal call numbers are used by OCLC member libraries. This paper discusses findings related to the use of the Dewey Decimal numbers. The use of the Library of Congress call numbers will be reported later.