Neuro-ophthalmologists frequently care for patients with idiopathic intracranial hypertension (IIH), although many questions remain unanswered regarding its diagnosis, pathogenesis, and treatment. The Friedman-Jacobson criteria for the diagnosis of IIH specify lumbar puncture (LP) opening pressure values that are largely based on experience with little supporting normative data. Until recently, there were sparse data to define normal values of the LP opening pressure in children. Papilledema, the sine qua non of IIH, may not always be present, but the frequency of true IIH without papilledema is controversial and the threshold for diagnosing it varies among clinicians. Concepts regarding the pathogenesis of IIH continue to evolve; venous hypertension is certainly implicated even though it is uncertain whether venous sinus stenosis is the cause or effect of increased intracranial pressure. The 2010 Jacobson Lecture discusses the evidence for some of the prevailing assumptions about normal lumbar puncture opening pressure, venous sinus stenosis, and the phenotypic continuum between chronic daily headaches and IIH.