Patients undergoing bilateral total knee arthroplasty (BTKA) may have higher complication rates and mortality than those undergoing a unilateral procedure (UTKA). To evaluate this hypothesis, we analyzed nationally representative data collected for the National Hospital Discharge Survey on discharges after BTKA, UTKA, and revision TKA (RTKA) between 1990 and 2004. The demographics, comorbidities, in-hospital stay, complications, and mortality of each procedure were compared. An estimate of 4,159,661 discharges (153,259 BTKAs; 3,672,247 UTKAs; 334,155 RTKAs) were included. Patients undergoing BTKA were younger (1.5 years) and had a lower prevalence of comorbidities for hypertension (versus UTKA), diabetes, pulmonary disease, and coronary artery disease (versus UTKA and RTKA). The length of hospitalization was 5.8 days for BTKA, 5.3 for UTKA, and 5.4 for RTKA. Despite similar length of hospitalization, the prevalence of procedure-related complications was higher for BTKA (12.2%) compared with UTKA (8.2%) and RTKA (8.7%). In-hospital mortality was highest for patients undergoing BTKA (BTKA, 0.5%; UTKA, 0.3%; RTKA, 0.3%). Patients undergoing BTKA had a 1.6 times higher rate of procedure-related complications and mortality compared with those undergoing UTKA. Outcomes for patients undergoing RTKA for most variables were similar to those for UTKA. BTKA, advanced age, and male gender were independent risk factors for complications and mortality after TKA. Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.