Probing of the nasolacrimal duct is a common procedure in children with congenital stenosis. Although simple probing of the nasolacrimal duct is successful in a majority of patients, a number of failures occur. In those temporary intubation of the nasolacrimal duct with a silicone drain may solve the problem. We performed silicone intubation in 11 infants under nasal endoscopic control. By this improved visualization of the inferior meatus, the procedure was facilitated. In four children the probe was unable to pierce the nasal mucosa and stayed in the submucosal space. An incision of the nasal mucosa was needed before the probe could be passed into the nasal lumen. We believe that this situation, inability to pierce the nasal mucosa, may explain a number of failures of simple probing. It is therefore advisable, especially if initial probing has failed, to repeat the procedure under endoscopic control.