In patients presenting with intracranial hypertension without hydrocephalus, mass lesions, and with normal cerebrospinal fluid (CSF) composition (pseudotumor cerebri syndrome), the diagnosis of intracranial sinus venous thrombosis (ISVT) has crucial etiological, therapeutic and prognostic implications. Utilizing two well-defined groups of pseudotumor cerebri patients, one with magnetic resonance imaging (MRI) or angiography confirmed ISVT (17 patients) and the other in whom ISVT has been excluded (idiopathic intracranial hypertension [IIH], 27 patients), we investigated the characteristics that might be helpful in distinguishing them. No clinical or auxiliary findings differed between the ISVT and IIH groups except for female gender and lower CSF protein level, which were significantly associated with the latter. While the syndrome pseudotumor cerebri could be due to multiple causes including ISVT, the term IIH should be restricted for patients with isolated intracranial hypertension attributable to no other neurological or systemic disease. Since CT frequently misses ISVT, patients with pseudotumor cerebri syndrome should undergo MRI and MR venography before being labeled as IIH. We conclude that Modified Dandy's Diagnostic Criteria of pseudotumor cerebri, formulated prior to MRI era, can no longer be applied for the diagnosis of IIH.