The entorhinal cortex is a key site of interneuronal communication between a variety of cortical and subcortical areas and hippocampal formation. Lesioning the entorhinal cortex is commonly used in studies of the hippocampal formation, animal behavior and neuronal plasticity. We have found that electrolytic destruction of the entorhinal cortex consistently produces limbic seizure activity in rats. The propensity of lesions in this area for producing seizure activity may facilitate insights into the normal function of this network of neural connections. This unexpected phenomenon represents a potential confounding variable for all researchers using this method for making brain lesions.