Suction drains provide an easy and feasible method for controlling hemorrhage after total knee arthroplasty. However, there has been no compromise regarding the optimum clamping time for these drains. We conducted a randomized clinical trial in 50 patients to compare 12-hour drain clamping and continuous drainage after total knee arthroplasty in terms of wound complications, blood loss, and articular arc of motion. To eliminate any other factor except duration of clamping, we chose to compare only knees belonging to a single patient and to restrict the study to those knees undergoing surgery due to osteoarthritis. From a total of 100 knees (50 patients) studied, the 12-hour-clamping method resulted in a significantly smaller amount of postoperative blood loss (p < 0.001). The passive ranges of motion and wound complications were not significantly different between the two groups.