Purpose To determine the efficacy of lacrimal balloon catheter dilatation in treating congenital nasolacrimal duct obstruction (CNLDO) as a primary procedure in children more than 18 months of age and in children who have failed lacrimal probing or silicone intubation. Design Retrospective, interventional case series. Participants Fifty-nine patients, ranging in age from 15 months to 9 years (mean, 35.6 months), with 73 lacrimal systems diagnosed with CNLDO who underwent nasolacrimal balloon catheter dilatation. Thirty-four lacrimal systems (46.5%) had no previous procedures, whereas 39 lacrimal systems (53.5%) had failed probing, silicone intubation, or both. Intervention Balloon catheter dilatation was performed following standard protocol, with a simplified regimen in most patients. Main outcome measures Clinical patency of the nasolacrimal duct after balloon dilatation was the main outcome measure and was defined as complete resolution of signs and symptoms (crusting, discharge, and increased tear meniscus). Age, inferior turbinate infracture, and Downe’s syndrome as related to the main outcome measure were also analyzed. Results Overall, 56 of the 73 lacrimal systems (76.7%) had complete resolution of symptoms. Twenty-seven of all 34 primary balloon catheter dilatations (79.4%) remained clinically patent, whereas 29 of all 39 secondary balloon catheter dilatations (74.4%) remained clinically patent after surgery ( P = 0.8165). Thirty-nine of 47 lacrimal systems (82.9%) in children older than 24 months remained clinically patent, whereas 17 of 26 lacrimal systems (65.4%) in children younger than 24 months remained clinically patent ( P = 0.1573). The mean age of patients with successful outcomes was 37 months, whereas the mean age of patients with failed balloon catheter dilatations was 32 months ( P = 0.3924). In the secondary procedure group, analysis showed that the mean age of success (32 months) was greater than the mean age of failure (18 months; P = 0.0491). Within the secondary group, 16 of 17 lacrimal systems (94.1%) older than 24 months were successful, whereas 13 of 22 lacrimal systems (59.1%) younger than 24 months were successful ( P = 0.0344). Conclusions Balloon catheter dilatation is an effective treatment for congenital nasolacrimal duct obstruction. In particular, balloon catheter dilatation in older children who failed previous probing is highly successful.