To utilize the Surveillance, Epidemiology, and End Results (SEER) registry to examine trends in grade assignment. Data from 411 325 patients from 1984 to 2003 were analyzed for grade migration and for cause-specific survival (CSS) as a function of grade. There has been a significant grade migration during the study period (P<0.001), principally from well-differentiated (WD) to moderately differentiated (MD) disease. Five-year CSS of MD and WD patients have converged, suggesting a decreasing role of grade as a prognostic factor. A grade migration from WD to MD assignment has occurred, suggesting that prognostic categorizations based on grade across eras may be difficult to interpret.