Nasal and sinus polyposis in the pediatric population is uncommon and its etiology is unclear. In this 11-year retrospective study, the authors describe the etiologic features and evaluate the effectiveness of endoscopic sinus surgery in 46 children. Patients were divided into three groups according to whether nasal and sinus polyposis was isolated (n = 14), or associated with either asthma (n = 5) or cystic fibrosis (n = 27). An allergy was present in 10% of patients with isolated polyposis, 80% of patients with polyposis associated with asthma, and 22% of patients with polyposis associated with cystic fibrosis. The indications for surgery were disabling symptoms, especially chronic nasal obstruction, rhinorrhea, and mouth breathing, and failure to respond to medical treatment. No surgical complications were encountered. Most patients reported improvement in quality of life with reduction of nasal obstruction in 83% of cases and rhinorrhea in 61%. Minor asymptomatic recurrence (i.e., a few micropolyps localized on the roof of the ethmoid cavity) was observed in 24% of the cases in this series, and major recurrence with the same functional symptoms as before surgery in 12%. However, recurrences were higher in patients with cystic fibrosis, because minor recurrence with no clinical manifestation was observed in 32% of these cases and major recurrence in 16%. Endoscopic sinus surgery must be decided in collaboration with the pediatric and pulmonary physicians, and must be performed skillfully. With a mean follow-up of 3.7 years, results in this series are encouraging.