BACKGROUND : Although postoperative spinal epidural hematoma is a rare complication, it can cause severe neurologic complications. Studies regarding biportal endoscopic spinal surgery, a type of minimally invasive spinal surgery technique, have been recently reported. The purpose of our study is to report the incidence and risk factors of postoperative hematoma after biportal endoscopic spinal surgery. METHODS : The subjects included 310 patients that underwent biportal endoscopic spinal surgery from 2015 to 2017. Magnetic resonance imaging (MRI) was performed in all patients before surgery, and also after surgery to identify epidural hematoma. Using electronic medical records, perioperative factors such as age, sex, operation name, operation level, water infusion pump usage, thrombin-containing hemostatic agent, and anticoagulant medication were statistically analyzed in the aspect of postoperative hematoma. RESULTS : The overall occurrence rate of postoperative hematoma was 23.6% (n = 94). A total of 304 levels (76.4%) were without hematoma according to the postoperative MRI among the total 398 levels. Six patients underwent revision surgery of hematoma evacuation. Female sex, old age (>70 years), preoperative anticoagulation medication, and usage of intraoperative water infusion pump were significantly correlated to the occurrence of postoperative hematoma. CONCLUSIONS : Although symptomatic postoperative hematoma was extremely rare at 1.9%, radiologic hematoma confirmed by postoperative MRI was higher at 23.6%. The perioperative risk factors of postoperative hematoma after biportal endoscopic spinal surgery include female sex, older age (>70 years), preoperative anticoagulation medication, usage of intraoperative water infusion pump, and surgery requiring more bone work (laminectomy or interbody fusion).