We report a 69-year-old woman who developed serious hydrocephalus after cervical laminoplasty for ossification of the posterior longitudinal ligament. The patient presented with approximately 50% spinal canal compromise pertaining to ossified lesion at C5 and C6 levels and subsequently underwent a C3-C7 open-door laminoplasty, followed by uneventful neurological recovery until 2 weeks postoperatively. Despite a favourable postoperative course, she presented with serious symptoms and signs of intracranial hypertension about 3 weeks after surgery. Computed tomography demonstrated the appearance of marked hydrocephalus, with no explainable cause. A ventriculoperitoneal shunt followed by removal of subdural fluid in the suboccipital fossa resulted in resolution of the clinical symptoms and of the hydrocephalus. It is important to be aware of the very rare occurrence of such intracranial neurological compromise after a cervical laminoplasty operation for long-standing ossification of the posterior longitudinal ligament.