Describes the history of the FBI's Uniform Crime Reporting (UCR) system and the data problems that it deals with in reporting crime and arrests. The report includes a description of the procedures used by the FBI to fill in gaps in the data (when they exist) and makes suggestions about how they might be improved. Since the FBI is moving to implement an improved crime and arrest reporting system, the National Incident-Based Reporting System (NIBRS), to replace the UCR, a study of deficiencies in UCR data should be of use in planning for the full implementation of NIBRS. The full report is based on a joint FBI-BJS workshop on UCR imputation procedures held in April 1997, and is a discussion paper prepared by Michael D. Maltz, University of Illinois at Chicago under the BJS Visiting Fellows Program.