Routine use of drains in total knee arthroplasty (TKA) is controversial. The aim of this study is to define the hourly risk of bleeding in the first 24 h following TKA using a survival study, to detect factors that might modify this risk, and establish a predictive model. In a retrospective study including 112 knees, patients with a coagulation disorder, platelet disease, or anticoagulation treatment were excluded. The risk factors studied included anesthesia score of the American society of anesthesiologists (ASA), proteinemia, total volume of fluid drained, and the use of low molecular weight heparin. The Kaplan-Meier test, Mantel-Haenszel test, and Cox regression analysis were used for the statistical calculations. The results indicate that the drains used in TKA can be removed within the first 18 h with a high degree of safety and low risk of persistent bleeding. The evolution of postoperative bleeding was independent of the factors studied.