Introduction: Colloid cysts of the third ventricle are rare benign intracranial lesions that are distinctly uncommon in the pediatric population. When located at the foramen of Monro, they can obstruct cerebrospinal fluid (CSF) flow and cause rapidly progressive obstructive hydrocephalus, a life-threatening neurosurgical emergency . Early diagnosis is essential, as thisrepresents a potentially reversible cause of raised intracranial pressure with excellentneurological outcomes following timely intervention. Case presentation: An 11-year-old previously healthy girl presented with recurrent vomiting for12 hours, associated with mild headache and a sensation of faintness. Within 3–4 hours, she developed a rapidly progressive decline in consciousness. On admission, her Glasgow Coma Scale score was 8/15. Endotracheal intubation was performed to secure the airway . Initially , her pupils were equal and sluggishly reactive, but subsequently became unequal. She hadhyperreflexia and developed systemic hypertension above the 95th percentile for age, height, and sex, together with bradycardia suggestive of Cushing’s response. She was transferred to a tertiary care hospital, where urgent neuroimaging revealed a cystic lesion at the foramen ofMonro causing acute obstructive hydrocephalus with cerebral edema. An urgent external ventricular drain was inserted for CSF diversion and intracranial pressure control, followed by definitive surgical excision of the cyst. Histopathology confirmed a colloid cyst. Her postoperative recovery was uneventful, and she was discharged without any neurologicaldeficit. Conclusion: Colloid cysts should be considered as a rare but reversible cause of acute obstructive hydrocephalus in children. Early identification, prompt neuro imaging, and timely neurosurgical interventions are lifesaving.