Eighteen percent (n = 59,038) of TJA patients underwent blood transfusion during their surgery, from 15% with single knee to 45% for bilateral hip arthroplasty. Multivariate analysis indicated that compared with the referent category of single knee arthroplasty, single hip had a significantly higher odds of blood transfusion (odds ratio [OR], 1.76; 95% confidence interval [CI], 1.68-1.83), as did bilateral knee (OR, 3.57; 95% CI, 3.20-3.98) and bilateral hip arthroplasty (OR, 6.17; 95% CI, 4.85-7.85). Increasing age (eg, age ≥80 years; OR, 2.99; 95% CI, 2.82-3.17), Medicaid insurance (OR, 1.36; 95% CI, 1.27-1.45), higher comorbidity index (eg, score of ≥3; OR, 2.33; 95% CI, 2.22-2.45), and females (OR, 1.75; 95% CI, 1.70-1.80) all had significantly higher odds of blood transfusion after TJA.