Objectives/Hypothesis: To evaluate the efficacy of surgical sphenopalatine artery occlusion (SAO) for treating intractable epistaxis, and identify factors associated with long-term success or failure of this procedure. Methods: A retrospective chart review of patients undergoing SAO surgery between January 1995 and 2005 was undertaken. Clinical and hematologic information, preoperative and surgical care, short-term complications, and long-term outcome were recorded. Binary logistic regression was used to identify risk factors for early re-bleeding, and log-rank statistics with Cox regression were used to identify risk factors for long-term operative failure. Results: Sixty-seven patients underwent 71 SAO operations. The average age at surgery was 56 +/- 18 years. Thirty percent of patients were being treated for hypertension, 19% were taking aspirin, and 11% were anticoagulated with warfarin. Many patients (46%) had > 72 hours of epistaxis before admission, and 25% required preoperative transfusion. There were 13 (19%) bilateral procedures, six patients underwent concomitant anterior ethmoid artery occlusion, and 12 patients had concomitant septoplasty. Eight patients had significant early re-bleeding. Platelet levels on admission and not using diathermy to occlude the sphenopalatine artery were independent risk factors for this (P values .03, and .02, respectively). Not using diathermy was also an independent risk factor for late operative failure on Cox regression, reducing the mean re-intervention-free interval from 94 +/- 7 to 32 +/- 7 months (P < .007; hazard ratio 6.4; 95% confidence interval 1.7-24.9).