Electroencephalographic abnormalities may occur in autistic spectrum disorders (ASD) even in the absence of clinical seizures. These abnormalities may vary from nonspecific changes to epileptiform abnormalities and are more common compared to the overall population. The level of intelligence is a significant risk factor for epilepsy in ASD. However, the relation between the functionality of the individuals with autism and the electroencephalographic (EEG) abnormalities, and the clinical significance of these abnormalities still remain relatively unclear. In this study we investigated the presence of EEG abnormalities in sixteen children diagnosed with high-functioning ASD. EEG recording was performed for at least 2 h and included at least 90 min of sleep activity. While none of the patients had clinical seizures, 5 patients (31.3%) were detected to have EEG abnormalities. Four of these were epileptiform (25%), and one patient developed seizure during follow-up. Our results support the fact that EEG abnormalities are observed at a higher rate also in ASD with a better functionality. The potential impact of EEG abnormalities on cognition and behavior, and the risk of epilepsy should be considered during long-term follow-up of these patients.