This study's objective was to evaluate changes of Jugular bulb oxygen saturation (SjVO2) during surgery for severe head injured patients. A prospective study was conducted on 50 severe head injured patients undergoing craniotomy surgery. Preoperative SjVO2 in jugular bulb was measured after anesthesia induction by a catheter connecting to CeVOX monitor. SjVO2 was observed continuously during sugery and recorded at different phases: before surgery (T1), after craniotomy (T 2), after durotomy (T 3), after removing hematoma (T 4) and in 30 minutes after surg.ery (T 5). SjVO2 was in the normal range in 52 percent of patients, reduced in 32 percent and increased in 16 percent of patients. SjVO2 increased significantly.during surgery, especially after craniotomy and durotomy compared to the preoperative phase (69.1 +/- 13.2 percent and 70.3 +/- 13.1 percent vs. 61.8 +/- 15.6 percent, P 0.05). SjVO2 did not change significantly in the patients with preoperative SjVO2 75 percent. In conclusion, SjVO2 increased significantly after craniotomy and durotomy in severe head injured patients with low or normal preoperative SjVO2 values.