An endonasal dacryocystorhinostomy (DCR) was followed by cerebrospinal fluid leakage and pneumoencephalocele in an 80-year-old female patient presenting four independent risk factors for an ethmoidal breach: severe septal deviation requiring forced reclining, a cranial insertion of the perpendicular plate of the ethmoid directly onto the cribriform plate, meningeal prolapse, and extensive osteoporosis of the skull base. The use of a Killian valve speculum to recline the nasal septum was probably the main cause of the anterior skull base fracture. The defect was repaired by a composite patch of septal cartilage, abdominal fat grafts, Surgicel, and inferior turbinate mucosa. Thirty-four months after surgery, there was no residual symptom. A narrow nasal fossa makes endoscopic DCR more difficult to perform. The use of a Killian valve speculum to enlarge the nasal fossa may carry a risk for structural damage to the skull base. A narrow nasal fossa may require an external DCR or a prior endoscopic septoplasty to facilitate an endonasal approach. Closing an ethmoidal defect causing cerebrospinal fluid leakage can be successfully achieved by an endonasal approach rather than by a more conventional neurosurgical method.