The long term results of probing for congenital nasolacrimal duct obstruction were reviewed using a parental questionnaire issued to both treated and age-matched control groups. On follow up 4-13 years after probing in childhood 30% of patients still had symptoms of epiphora or discharge. Surprisingly, a similar high symptom rate was found in the controls, such that there was no statistically significant difference in the rate of symptoms between the two groups. Probing had therefore apparently reduced the symptom rate to a level close to normal for the age group concerned. All studies on the incidence of congenital nasolacrimal duct obstruction must be interpreted with reference to the known high rate of spontaneous resolution as a clear trend has been demonstrated towards a lower incidence of symptoms the longer the follow up after probing. This finding would support a policy of delay before further intervention in patients with mild residual symptoms after a technically successful probing.