In 20 patients with benign intracranial hypertension (BIH) a study of the P100 latency of visual evoked potentials (VEP) was carried out. At admission only 5 patients showed abnormal latencies. The mean of the P100 latencies in patients was significantly increased as compared with controls. Latencies persisted relatively prolonged once the funduscopy had become normal. In the last investigation, one year after BIH had disappeared, the latencies in patients were already similar to those in the control group. On the other hand, no patient with normal latencies had visual sequelae. Sequelae also did not develop in patients in whom initially prolonged latencies progressively returned to normal during the evolution. Sequelae developed in one patient in whom latencies became progressively prolonged. In that case the increased latencies preceded the fall in visual acuity. These data may be useful to evaluate visual function in patients with BIH.