Periodic lateralized epileptiform discharges (PLEDs) had been debated whether it is ictal or non-ictal phenomenon. As most of PLEDs occur in patients with acute structural lesions, some epileptologists prefer PLEDS as a non-ictal phenomenon, rather an obscure epiphenomenon of etiological diseases. But, almost half of the patients with PLEDs do not have acute structural lesions in the brain and metabolic disorders or old CNS lesions may cause PLEDs and even more, no brain lesion was identified in some patients. There are many data supporting PLEDs as ictal phenomena. Occurrence of PLEDs usually accompanied by decreased mentality and is improved as PLEDs disappeared. Current SPECT study showed marked hyperperfusion in the lesion side of PLEDs, that is striking evidence of PLEDs as ictal phenomena. Also careful review of EEG with PLEDs revealed it is a dynamic process rather than a static state. Despite of these evidences, as PLEDs are an end-stage of animal status epilepticus models, it may be a transition of ictal to interictal state.