Mutations at FRAXA and FRAXE loci are due to expansions of a CGG trinucleotide repeat and are characterized by mental retardation. Here we report a pilot screening survey by means of cytogenetic and molecular methods of 433 unrelated retarded individuals and their parents of Hellenic origin coming from various parts of Greece and Cyprus. The purpose of the study was to estimate the frequency of FRAXA mutation in individuals with nonspecific mental retardation without family history and phenotypic stigmata in the Hellenic population. Five FRAXA-positive children (1.15%) were identified, of whom four were found to carry a full mutation and one a premutation. Furthermore we present preliminary data on a screening of FRAXE mutation frequency. We screened 257 male patients with nonspecific mental retardation, finding none positive for FRAXE mutation.