A series of 49 cases with cerebral venous thrombosis (CVT) and a series of 17 cases with benign intracranial hypertension (BIH) without CVT, both observed between 1973 and 1983, have been compared. Papilledema has been found in 100% of BIH and 28.5% of CVT, visual acuity loss in 52% of BIH and 6% of CVT, obnubilation in 0% of BIH and 65% of CVT. Cerebrospinal fluid, EEG, cerebral angiography and Scanner were normal in all cases of BIH, while in CVT the same investigations were abnormal in respectively 90%, 100%, 100% and 54% of cases. Prognosis was excellent in BIH with only one residual mild loss of visual acuity. Recurrences occurred in 18% of BIH. Among CVT 18% died, 23% developed neurological sequelae, 59% totally recovered. There was no recurrence. On the basis of this comparative study we emphasize the following points: 6% of CVT only follow a course of BIH from end to end, according to Johnston and Paterson's diagnostic criteria of BIH. These cases concern only thrombosis of lateral sinuses. Other cases of CVT rather deal with patients admitted in neurosurgical units on emergency. Diagnosis of CVT is a difficult one and prognosis is still serious in spite of the use of Heparin. 85% of BIH are irrelevant to CVT. BIH is a "quiet" intracranial hypertension without trouble of vigilance. Prognosis is really good if diagnosis is early made, in spite of possible multiple recurrences. Treatment consists of CSF subtraction, preferably through external lumbar drainage, and Acetazolamide prescription. Head injuries and hormonal imbalance in women are two common etiologies of BIH and CVT.(ABSTRACT TRUNCATED AT 250 WORDS)