The aim of this study was to determine the correlation between pre- and postsurgical loss of blood and blood components among patients undergoing treatment of facial deformities by bilateral parasymphyseal osteotomy (BPsO).The pre- and postoperative values of blood components were determined in 30 facial deformity patients who underwent orthognathic surgery by hypotensive anesthesia. Correlations among the blood loss, sex, age, operation time, and reduced values of blood components were assessed by a correlation matrix. The mean blood loss and operation time were 437.5 (± 52.5) mL and 355.8 (± 209.42) minutes, respectively. Two patients included in this study had required blood transfusion. The mean reduced red blood cell (× 10/μL), hemoglobin (g/dL), and hematocrit (%) were -1.02, -2.98, and -9.18, respectively. There was no significant correlation between blood loss and other related factors (eg, age, operation time, and reduced blood components). All patients, however, showed significantly lower values of blood components after surgery. In conclusion, no significant factor was associated with blood loss and reduced blood components among patients undergoing BPsO. Furthermore, hypotensive anesthesia is a well-accepted method to reduce blood loss during orthognathic surgery.