In a prospective study, 24 consecutive patients with pseudotumor cerebri were followed for an average of 49 months with regular neurologic and ophthalmologic examinations. At the first examination the intracranial pressure was between 18 and 45 mm Hg; several patients had pressure waves up to 70 mm Hg and decreased conductance to cerebrospinal fluid outflow. In the majority, medical treatment, usually with diuretics and acetazolamide, induced a rapid relief of symptoms, but about 25% had a more protracted disease course with persistent headache, asthenia and memory disturbances interfering with daily life. Five patients required a shunt operation. Chronic changes of the optic disc developed in nearly half the patients, and one had optic atrophy and severe visual impairment. Repeated measurements of the intracranial pressure and conductance to cerebrospinal fluid outflow showed that abnormalities can persist for a long time, even in cases without symptoms of intracranial hypertension.