Although the majority of work-related homicides are routinely reported in the United States, information on non-fatal events is less complete. Comprehensive surveillance of non-fatal events depends on understanding reporting trends to different agencies. This study characterizes workplace assaults reported to police and through employers in eight southern California cities. Employers' reports filed from October 1, 1994, through January 31, 1995, and police reports filed from June 1, 1994, through March 31, 1995, that involved a non-fatal workplace assault injury were included. Reports from police and employers were linked, and annualized rates combining non-duplicative reports were calculated and event characteristics compared. The combined annualized rate of workplace assault injury for the eight cities was 184.6 per 100,000 workers, which was almost twice the rate found in either reporting source individually. Police reports differed from employers' reports by industry and occupation of victim but not type of event or weapons used. Examination of multiple reporting sources for non-fatal workplace assault injuries is essential to identifying the magnitude of these events. Understanding trends in reporting is important for the effective design of prevention programs.