Endoscopic sinus surgery (ESS) is indicated in select pediatric patients with medically refractory sinus disease. Our objectives were to examine indications and rates of readmission following ambulatory pediatric ESS and identify specific subgroups that may benefit from inpatient admission.Retrospective database review.The Pediatric Health Information Systems (PHIS) 2004-2016 database was retrospectively reviewed for patients age <18 years who underwent ambulatory ESS between January 2011 and December 2016 and were readmitted within 30 days postoperatively. Data regarding demographics, extent of surgery, comorbidities, adjunctive procedures, and cost were collected. A multivariable mixed-effects logistic regression model was employed for analysis.We identified 3,669 unique pediatric ESS cases with 128 readmissions within 30 days (3.5%; 95% confidence interval [CI]: 2.9%-4.1%). Median cost of readmission was $980 (mean, $5,890; standard deviation, $13,421). The most common indication for readmission was epistaxis (17.2%), followed by nausea/abdominal pain (14.1%). Respiratory infection (13.3%) and sinusitis (10.2%) presented a combined readmission rate exceeding that of epistaxis alone. Multivariable analysis indicated age <3 years (odds ratio [OR]: 3.41, 95% CI: 1.96-5.93) and a prior diagnosis of asthma (OR: 2.88, 95% CI: 1.99-4.18) or cystic fibrosis (OR: 1.57, 95% CI: 1.00-2.44) significantly increased the risk of readmission. Extent of ESS and simultaneous adenoidectomy, septoplasty, or turbinate reduction had no significant impact on readmission rates.ESS is a relatively safe outpatient surgical procedure in pediatric patients, with an overall readmission rate of 3.5%. Clinicians should consider careful preoperative evaluation of very young patients and those with cystic fibrosis or asthma to optimize perioperative management and determine if postoperative admission is warranted, given their significantly higher readmission rates.NA Laryngoscope, 2019.