OBJECTIVE To evaluate the safety and effectiveness of balloon dilation for the treatment of congenital lacrimal system obstruction. METHODS Fluoroscopically guided balloon dilation was attempted in 20 eyes of 16 patients with an age range of 12-78 months (mean, 33 mo) for congenital lacrimal system obstruction. Fifteen eyes had complete obstruction at the valve of Hasner, three eyes had completely obstruction at the junction between the lacrimal sac and the nasolacrimal duct, and two eyes had partial obstruction at the nasolacrimal duct. Under general anesthesia, a ball-tipped guide wire was introduced through the superior punctum into the inferior meatus of the nasal cavity and pulled out through the naris with use of a hook. A deflated 3-mm-diameter balloon catheter was then advanced in a retrograde direction and the balloon was dilated. Every patient underwent an ophthalmic evaluation before the procedure and was scheduled to be followed with office examination at 1, 3, and 6 months after the procedure. RESULTS There were no major complications. "Technical success" was defined as free passage of contrast medium through the entire lacrimal system to the nasal cavity. The procedure failed in one eye. After balloon dilation, all 19 eyes in which technical success was achieved showed improvement of epiphora. During the follow-up period of 2-33 months (mean, 16 mo), all eyes maintained improvement of epiphora and needed no further treatment. CONCLUSIONS Balloon dilation is a safe and effective therapeutic technique for the treatment of congenital lacrimal system obstruction.