We analyzed the National Hospital Discharge Survey to elucidate temporal changes in the demographics, comorbidities, hospital stay, in-hospital complications, and mortality of patients undergoing primary total knee arthroplasties (TKAs) in the United States. Three 5-year periods were created (1990-1994, 1995-1999, and 2000-2004), and temporal changes were analyzed. The number of TKAs performed increased by 125% for the 3 periods. The increasing proportion of younger patients was accompanied by a concomitant decrease of Medicare-insured patients. Length of stay decreased from 8.44 to 4.18 days. An increase in the proportion of discharges to long-term and short-term care facilities and in procedures performed in small hospitals was noted. Although the prevalence of procedure-related complications decreased over time, comorbidities increased. Despite a decrease in mortality from the first to the second study period (0.50% vs 0.21%), a slight increase was noticed more recently (0.28%). We identified significant changes in most variables studied.