We report a series of eight cases that show a close resemblance to, but are not identical with, pseudotumor cerebri (PTC) as normally defined. The majority of these cases are characterized by raised intracranial pressure without ventriculomegaly. They include two cases of cranial venous outflow obstruction in which clinical or radiologic abnormalities precluded the diagnosis of PTC proper (cases 1 and 2); one case of chronic meningitis in which an abnormal cerebrospinal fluid (CSF) composition precluded the diagnosis of PTC (case 3); two cases without either papilledema or a measured increase of CSF pressure, which in other respects, particularly in response to treatment, resembled PTC (cases 4 and 5); and three cases of what is thought to represent an infantile form of PTC (cases 6 through 8). The purpose of the analysis of these cases is twofold. First, it is argued that these cases throw light on the mechanism of PTC itself, supporting a concept of a disturbance of CSF circulation in this condition, and that they are themselves illuminated by considerations of typical PTC. Second, the cases are used to frame a proposed classification of the pseudotumor syndrome aimed at broadening the diagnostic criteria applied currently to PTC. It is suggested that the pseudotumor syndrome has a single underlying mechanism (disturbed CSF circulation) and that recognition of this mechanism not only clarifies the pathophysiologic processes of PTC but also has important diagnostic and therapeutic implications.