In this retrospective study authors compare the success rate of nasal endoscopic-assisted probing between younger (three years and below) and older (three years and above) children with membranous nasolacrimal duct obstruction and its correlation with the thickness of the membrane at valve of Hasner. Thirty-four patients and 38 lacrimal systems of age ranging from six months to eight years were included in the study. They were divided in two groups; younger (group Y, 20 cases) for three years and younger and older (group O, 18 cases) for three years and above. All cases were operated by a single surgeon. Cases with punctal stenosis, lid malposition, canaliculitis, craniofacial anomalies, bony obstruction and complex congenital nasolacrimal duct obstruction were excluded. The membrane at the valve of Hasner was classified as thin if the probe was visible through the membrane and if the probe could perforate the membrane easily without resistance. The membrane was classed as thick if visibility of the probe was poor and if the complete membrane was not incised by the probe and had to be cut with a sickle knife. None of the cases were intubated. Overall success was 35 out of 38 (92.1%). Nineteen cases (95%) in group Y and 16 cases (88.88%) in group O had complete resolution. This was not statistically significant (p=0.59). The membrane was thin in 50% cases in group Y and 66.66% of cases in group O. The authors conclude that the membrane at valve of Hasner is of variable thickness and has no correlation with age of patient or with success of probing if carried out with endoscopic guidance. The limitations of the study are; retrospective design, a small sample size and total length of follow-up not known.