Abstract: The purpose of this randomized prospective study was to determine the effects of head position on postoperative conjunctival swelling (chemosis) after prone spinal surgery. On the basis of the head position, 140 patients scheduled for prone lumbar surgery were randomly allocated into 2 groups: head neutral group (n = 70) versus Head Down (HD) group (n = 70). Head position was defined as neutral when the imaginary line from the occipital protuberance to the top of C7 spine process is parallel to the operating table. HD position was maintained by adjusting the height of the prone headrest 5 cm lower than neutral position. Chemosis was evaluated after surgery. The overall incidence of chemosis in the Head Neutral group was significantly lower than the Head Down group [25 (35%) vs 48 (68%), p = 0.003]. The severity of chemosis, which was graded as none, mild, moderate and severe, showed statistically significant difference between the head neutral group [45 (65%), 14 (20%), 7 (10%), 4 (5%), respectively] and Head Down group [22 (32%), 13 (18%), 25 (36%), 10 (14%), respectively, p<0.05]. This result suggested that neutral head position was useful in decreasing the development of postoperative chemosis after prone spinal surgery.