BACKGROUND The placement of external ventricular drainage (EVD) to treat hydrocephalus secondary to a cerebellar stroke is controversial because it has been associated to upward transtentorial herniation (UTH). This case illustrates the effectiveness of endoscopic third ventriculostomy (ETV) after the ascending herniation has occurred. METHODS A 50-year-old man had a cerebellar stroke with hemorrhagic transformation, tonsillar herniation, and non-communicating obstructive hydrocephalus. Considering that the patient was anticoagulated and thrombocytopenic, an EVD was placed initially, followed by clinical deterioration and UTH. We performed a suboccipital craniectomy immediately after clinical worsening, but the patient did not show clinical or radiological improvement. On the 5th day, we did an ETV, which reverses the upward herniation and hydrocephalus. The patient improved progressively with good neurological recovery. CONCLUSIONS ETV is an effective and safe procedure for obstructive hydrocephalus. The successful resolution of the patient's upward herniation after the ETV offers a potential option to treat UTH and advocates further research in this area.