To evaluate the role of induced hypotension during maxillary downfracture osteotomy on the requirement for blood transfusion, duration of operation and induced anaemia in bimaxillary surgery.45 young orthognathic patients were operated under hypotensive anaesthesia between 2004 and 2006. Operations were LeFort I osteotomies (n=45), bilateral sagittal split osteotomies (BSSO) (n=42), segmental osteotomies (n=3), tongue reduction (n=1), genioplasties (n=15), digastric myotomies (n=2), and bone grafts were the supplementary procedures. Pre-postoperative haemograms, intraoperative blood loss, and duration of operations were the studied parameters. Statistical analysis was performed using SPSS 11.5 for Windows.None of the patients received a blood transfusion. Mean blood loss was 377±111.2mL with the range of 180mL to the maximum of 625mL. Mean duration was 267.1±61.2min with minimum of 180min and maximum of 400min. Mean preop Hb level was 14±1.9g/dL with the range from 10.3g/dL to a maximum of 17.2g/dL. Mean postop Hb level was 11.8±2g/dL with a range of 8.2–16.2g/dL levels. Preop erythrocyte counts were 435.3±18.2 and 416.4±16.1 (×104/mcL) on the first postop day.Transfusion in bimaxillary orthognathic surgery could be prevented by induction of hypotension during maxillary downfracture.