Electroclinical dissociation is a phenomenon in which the clinical component of a seizure occurs at times with or without an electrical correlate. The epidemiology of this observation was studied in a neonatal intensive care unit from July, 1983 to December, 1988. Infants demonstrating electroclinical dissociation were compared to those having exclusively electroclinical seizures. Sixteen percent of infants with electrographically-confirmed seizures and 19% of 243 analyzed seizures demonstrated electroclinical dissociation. The two groups revealed very few differences with respect to perinatal factors, etiology, and outcome. The subsequent electroencephalographic background was more disturbed in the electroclinical dissociation group, but did not correlate with clinical outcome. Extremity movements occurred at a statistically significant higher rate during electroclinical seizures. Electroclinical dissociation seizures arise from foci not consistently reflected in surface electrodes.