Purpose: Due to the pneumoperitoneum, intraoperative bleeding is relatively limited during laparoscopic surgery. During robot-assisted laparoscopic radical prostatectomy (RLRP), after opening the bladder neck, the urine volume is usually incorporated in the estimated blood loss (EBL). The purpose of this study is to compare with EBL and calculated blood loss (CBL) after RLRP. Patients & Methods: Between July 2005 and April 2008, we performed 268 consecutive RLRP by single surgeon. Of these, 260 patients who did not receive blood transfusion became the subjects. We compared with EBL taken from the anesthesia report and CBL calculated from the following formula. EBV is the estimated blood volume and assumed to be 70cm3/kg. Hi and Hf are the preoperative haematocrit and the postoperative day one morning hematocrit. (3) Tu is the sum of autologous whole blood (AWB), packed red blood cells (PRBC), and cell saver (CS) units transfused. CBL=(EBV×(Hi-Hf)/((Hi+Hf)/2)+(500×Tu). Results: The mean (±SD) age and the mean operative time were 63.3±7.7 years and 204.8±38.1 minutes. The mean Hi and Hf were 42.0±4.3% and 36.1±5.4%. There were significant differences between Hi and Hf (p=0.000). The mean EBL and CBL were 327.4±220.8 mL and 748.5±757.4mL. There were significant differences between EBL and CBL (p=0.000). Conclusions: During RLRP, EBL estimated by anesthesiologists may underestimate CBL calculated by standard calculation. This discrepancy may be due to the hemodilution by intravenous fluid replacement postoperatively, and not by the actual postoperative hemorrhage after elimination of pneumoperitoneum.