The aim of the study was to investigate if preoperative blood flow velocity in femoral vein in different positions of the hip during total hip arthroplasty (THA) is a predictor of postoperative deep vein thrombosis (DVT). In patients undergoing THA, blood flow velocity and diameter of proximal femoral vein on THA side were measured preoperatively in four flexion positions of the hip. After THA, patients were followed up for 42 days for DVT occurrence, and clinical features of patients with and without postoperative DVT were compared. The mean blood flow velocity in maximal flexion (90º+) preoperatively was significantly lower in patients with postoperative DVT (19/103) compared to patients without it (8.4±2 cm/s . 10.6±2.3 cm/s; p<0.001). Using the receiver operating characteristic curve analysis, the cut-off value for blood flow velocity during maximal flexion was 8.24 cm/s. In addition, anesthesia duration, duration of surgical position of the patient, body mass index, amount of blood transfused after surgery, and clinical signs of DVT were markedly different between patients with and those without postoperative DVT. Blood flow velocity in femoral vein in maximal flexion of the hip (90º+) measured prior to THA is an independent predictor of postoperative DVT.