The relationship between the library and its patrons is damaged and the library's reputation suffers when returned items are not checked in. An informal survey reveals librarians' concern for this problem and their efforts to combat it, although few libraries collect objective measurements of errors or the effects of improvement efforts. Brigham Young University's Harold B. Lee Library is engaged in a quality improvement effort that includes the use of statistical process control and has resulted in an 86% reduction in errors over a two-year period. BYU's experience demonstrates the importance of objective measures in ensuring service quality. (Contains 2 tables and 3 figures.)