Summary: A clinical and EEG study of 12 fragile-X syndrome subjects (six with epilepsy) is presented. All subjects had clinical-family history examinations. EEG evaluations, and karyotyping. Spikes were present in the sleep EEG of one nonepileptic and four epileptic subjects; these spikes were similar in location, occurrence. voltage, frequency, and morphology (and similar to those of the Rolandic spikes). These data, together with the clinical similarities (type of epilepsy, responses to drugs. ages of seizure onset, etc.). have resulted in the postulation of EEG characteristics of epileptic and nonepileptic fragile-X patients. However, further studies with fragile-X patients are needed to confirm this hypothesis.