Focal cortical dysplasias (FCD) are one of the most common causes of drug-resistant epilepsy. Morphological changes in the focal cortical dysplasia tissues obtained from epileptic patients during surgical interventions were analyzed. Eleven specimens of the cerebral cortex with FCD areas were explored. There were a variety of light optical and ultrastructural abnormalities affecting different portions of the cortical arrangement, as well as a considerable heterogeneity in these changes. Special emphasis was placed on morphological correlations between excitation and inhibition processes when possible mechanisms responsible for the epileptogenicity of dysplasia cells were assessed. The findings suggest that there is a preponderance of FCD tissue excitation processes along with depressed inhibition processes.