We studied reversed optokinetic nystagmus (OKN) in 31 patients and found that it is actually the patient's own gaze-modulated spontaneous nystagmus shifted to the primary position of gaze by optokinetic stimulation. Two of our 31 patients were known to have congenital nystagmus. Most of the 29 others were adults who presented with neurological symptoms and nystagmus and were therefore suspected of having posterior fossa lesions. However, their nystagmographic findings and benign natural history suggest that they also had congenital nystagmus, which was unrecognized until they developed incidental neurological symptoms. These cases support the view that reversed OKN is pathognomonic of a benign, probably congenital, nystagmus.