Our objective was to compare outcomes (anesthesia time, total operative time, tourniquet time, duration of hospital stay, 90-day complication rate, and transfusion rates) of patients with total knee arthroplasty (TKA) who underwent bariatric surgery before or after TKA. One hundred twenty-five patients were included: TKA before bariatric surgery (group 1; n = 39), TKA within 2 years of bariatric surgery (group 2; n = 25), and TKA more than 2 years after bariatric surgery (group 3; n = 61). Patients with TKA more than 2 years after bariatric surgery had shorter anesthesia and total operative and tourniquet times than other groups; differences were significant between groups. Ninety-day complication and transfusion rates approached but did not meet statistical significance. Ninety-day complication rates and duration of hospital stay did not differ significantly between the 3 groups. The level of evidence was level II (cohort study). © 2012.