Patients with large prolactin (PRL)-secreting pituitary adenoma often have symptoms due to varying degree of hypopituitarism and/or mass effect on visual structures, while presentation with hydrocephalus is extremely uncommon. Even more exceptional is the development of the syndrome of intracranial hypertension as a consequence of tumor obstruction of the cerebrospinal fluid circulation. In this report, we describe a 26-year-old man who was referred to the emergency department of our hospital because of headache, nausea, and vomiting. Clinical and radiological assessment led to the diagnosis of obstructive hydrocephalus caused by a giant macroprolactinoma. The patient received a temporary external ventricular drainage to relieve the symptoms of intracranial hypertension. The same day, after we received the result of the basal PRL level, medical treatment with cabergoline was initiated. A prompt response to the drug ensued with resolution of the obstructive hydrocephalus, which allowed removal of the external ventricular drainage. Initial shrinkage of the mass was already noted on a magnetic resonance imaging performed 12 days thereafter. Subsequent medical treatment led to progressive and marked shrinkage of the tumor. Eighteen months after presentation the patient was well while on cabergoline treatment and showed no symptom attributable to compression of the surrounding nervous structures. Our report confirms that, even in cases of giant sellar mass with neurological symptoms, a rapid hormonal evaluation is mandatory. If a macroprolactinoma is diagnosed, treatment with dopamine agonists can lead to prompt clinical amelioration and shrinkage of the tumor, with eventual resolution of neurological symptoms.