OBJECTIVES: Absorbable hemostatic agents are commonly used after endoscopic sinus surgery (ESS). MPH (microporous polysaccharide hemospheres) is a novel hemostatic powder that is rapidly absorbed. The goal of this study was to examine the effects of MPH on bleeding after ESS. STUDY DESIGN: Randomized, controlled, single-blinded. SETTING: Tertiary university hospital. SUBJECTS AND METHODS: Patients undergoing bilateral (symmetric) ESS for CRS by the same surgeon were randomized to unilateral treatment with MPH at surgical conclusion. The untreated opposite side served as a control. All patients received standard postoperative management. Patients completed symptom diaries using visual analog scales (VAS, scored out of 100) at baseline and through postoperative day (POD) 30. Outcomes including bleeding, pain, obstruction, and nasal discharge were recorded separately for left and right sides. RESULTS: Forty patients (19 men, 21 women) with an average age of 48.3 years were included. There were no complications, and all patients were discharged home the same day. The mean bleeding score on POD one for MPH-treated sides was 22.5 vs 39.0 for untreated controls (mean reduction 16.5, P < 0.0001, 95% CI −23.2 to −9.7). The scores for bleeding at baseline and at all other post-treatment days were not significantly different ( P > 0.05). There were no other significant differences between MPH-treated and control sides in any other variables measured. CONCLUSION: The use of MPH after ESS results in significantly less bleeding in the early postoperative period with no increase in pain, obstruction, or nasal discharge. Patients treated with MPH follow a normal postoperative recovery otherwise.