Clinical and neurophysiological findings for 28 patients with mental retardation, autism, and epilepsy were described. Correct classification of seizure type and epileptic syndrome (when possible), etiology, severity of autism and epilepsy, EEG findings, and neuroimaging findings were given. No particular epileptic syndrome was found to be more frequently correlated to autism, severity of autism was not correlated with a more pronounced tendency to develop seizures, and females with autism were more frequently affected by seizures than were males. In conclusion, the risk for epilepsy does not seem to be correlated to autism itself, but the same noxious event induces autism and epilepsy. The severity of epilepsy is strictly correlated with its etiopathogenetic mechanisms.