We used two strategies to investigate a possible link between predisposition for epilepsy and mutations in the fragile X mental retardation-1 gene. The first entailed performing electroencephalography on 14 patients with an amplification in the fragile X mental retardation-1 gene, and the second involved molecular genetic analysis of the fragile X mental retardation-1 gene in 16 children with benign childhood epilepsy with centrotemporal spikes (BECT, Rolandic epilepsy). Fourteen young male patients with fragile X syndrome, verified by a full mutation in exon 1 of the fragile X mental retardation-1 gene, were studied by electroencephalography. In eight boys aged between 4-8 years we observed focal sharp waves, activated by sleep. In six of these patients, partial seizures occurred during sleep. We detected no epileptiform electroencephalographic abnormalities under the age of 4 and over the age of 8. In 16 children with Rolandic epilepsy who were studied for fragile X gene mutations, one boy proved to carry a fragile X premutation. In the waking state electroencephalography of a 5-year-old girl with a premutation in one of her fragile X mental retardation-1 genes, we found groups of generalized spike wave complexes. Our observations suggest a possible impact of the fragile X mental retardation-1 gene mutations on brain maturation and epileptogenesis.