Fragile X syndrome (FXS) is a neuro-developmental disorder characterized by intellectual disabilities and autism spectrum disorders (ASD). Expansion of a CGG trinucleotide repeat (>200 repeats) in the 5'UTR of the fragile X mental retardation gene, is the single most prevalent cause of cognitive disabilities. Several screening studies for FXS, among individuals with ID from different ethnic populations, have indicated that the prevalence of the syndrome varies between 0.5 and 16 %. Because the high co-morbidity with autism, we have conducted a screening study of the cohort from CHARGE, a large-scale, population-based, case control study. We have identified six subjects carrying an expanded allele, which emphasize the importance of screening for FXS in a population with intellectual disabilities and ASD.