Purpose To determine the success rate of nasolacrimal duct probing for the treatment of congenital nasolacrimal duct obstruction and to identify the age at which the success rate decreases. Methods Records for probing procedures from 2005 to 2010, over a 56-month period, were reviewed. Successful probing was defined as complete resolution of epiphora 3 months after treatment. Success rates were compared between children <3 years of age and children ≥3 years of age at the time of the procedure. Results A total of 168 eyes (128 children, mean age 32.2 ± 23.8 months) had undergone a probing procedure, and the overall success rate was 72%. Children aged <36 months had a success rate of 78%; children aged ≥36 months had a success rate of 50%. Multivariate analysis demonstrated that age at the time of procedure was a significant risk factor for failed probing (P = 0.035; OR, 1.67; 95% CI, 1.04-2.69), whereas sex and bilateral surgery were not. Conclusions The success rate of primary probing for congenital nasolacrimal duct obstruction was significantly reduced when performed on children ≥3 years of age.