OBJECTIVE:To analyze the clinical and EEG findings of patients with multifocal periodic lateralized epileptiform discharges (PLEDs). METHODS:EEGs containing multifocal PLEDs (3 or more foci of PLEDs) were reviewed. Thirty-five patients (15 males and 20 females), from 2.5 months to 91 years old, met the criteria for multifocal PLEDs. RESULTS:The disease processes identified in the patients included vascular lesions in 9, central nervous system infections in 7, metabolic/toxic disorders in 6, exacerbation of a chronic seizure disorder in 6, hypoxic ischemic insults in 3, and fat embolism, paraneoplastic encephalitis, cerebral metastasis, and multiple sclerosis in one each. Twenty patients died. Detection of the spatiotemporal distribution of multifocal PLEDs was facilitated by the use of Laplacian montages. CONCLUSIONS:Multifocal PLEDs were recorded in 35 patients and were associated with processes resulting in diffuse or multifocal cerebral dysfunction. Multifocal PLEDs indicate a significant disturbance of cerebral function and are associated with a mortality rate of 57%.