Purpose To report the incidence of intranasal abnormalities in children with nasolacrimal duct (NLD) obstruction and the results of treatment, which included nasal endoscopic removal of abnormal tissue. Methods Nasal endoscopy was performed prospectively in 22 infants with mucoceles; in 97 children ≥ 18 months at the time of initial NLD probing; and in 59 children with persistent NLD obstruction after previous probing. Endoscopic removal of abnormal tissue was performed in addition to NLD probing or balloon-catheter dilation. Results NLD cysts were found in 22 of 22 (100%) infants with mucoceles. Cysts or other abnormalities of the distal duct were found in 6 of 97 (6.2%) children ≥ 18 months at the time of initial probing and in 5 of 59 (8.5%) children whose previous NLD probing was unsuccessful. Surgery was successful in 91% of patients. Conclusion Nasal endoscopy identified intranasal anatomic abnormalities of the distal nasolacrimal duct uniformly in infants with mucoceles and in 6% to 9% of older children with complicated NLD obstruction. Treatment, including endoscopic removal of abnormal tissue, was successful in most patients. The use of nasal endoscopy may improve the treatment of patients with these disorders.