Summary: Introduction. The pseudotumor cerebri syndrome (PTC) is a clinical entity of unknown etiology affecting mainly young, obese women. The major morbidity factor in this condition is the possibility of vision loss, initially considered to be low, but now known to affect a significant proportion of patients. Clinical case. We describe a case of PTC in a young, obese black women who presented with headache, transient visual blurring and diplopia. Besides obesity, there where no other relevant clinical findings, namely other pathologies and history of medication use. An extensive analytical workup was negative and the CSF showed no abnormalities, aside from increased pressure. Brain MRI was also normal. The clinical course was progressively worse, consisting of rapid vision loss associated with an intracranial pressure of over 850 mmH2 O, despite treatment with diuretics (acetazolamide, furosemide and spironolactone) in therapeutic dosage. Eventually, the patient needed the rapid implantation of a lumboperitoneal shunt to prevent blindness, and went on to make a nearly full recovery. Conclusions. In all major series of PTC, loss of vision has been reported to occur in a significant percentage of patients, and cases have been described in which a catastrophic course with rapid progression to near blindness has led to the introduction of the designation of ‘malignant’ pseudotumor cerebri. We believe that such cases, although rare, need to be recognized as the malignant end of the spectrum of PTC, and that their management constitutes a neurological emergency.