Pseudomigraine with pleocytosis is a benign and autolimited syndrome. The etiology has been related to viral infection, but its pathophysiology is not yet well identified. To investigate this point, and to see if there were changes in cerebral blood flow (as in migraine), we performed single photon emission computed tomography (SPECT) studies in four patients who fulfilled the diagnostic criteria for this syndrome. This was done during the acute phase and we repeated SPECT after resolution of the syndrome in two of them. We found a reduction in brain blood flow on the side of origin of the neurological deficits during the acute phase. This normalized after recovery of the syndrome. The finding suggests that the neurological deficits in this syndrome could be produced by a spreading depression-like mechanism similar to that proposed for migraine with aura.