Purpose: To conduct a systematic review of literature regarding population-based screening for fragile X syndrome in newborns and women of reproductive age, either before or during pregnancy. Methods: Seven electronic databases were searched for English language studies published between January 1991 and November 2009. Data extraction was performed for all included studies. Results were synthesized using a narrative approach. Results: One article that examined offering newborn screening for fragile X syndrome and 10 that examined the offer of fragile X syndrome screening to women of reproductive age were identified. Two of these articles also addressed psychosocial aspects of population screening for fragile X syndrome such as attitudes to screening and experiences of screening, and a further nine addressed these issues alone. Studies exploring psychosocial issues demonstrated challenges for counseling arising from a lack of awareness or personal experience with fragile X syndrome in the general population. Conclusions: Targeted counseling and educational strategies will be essential to support women from the general population. It is crucial that future studies offering screening for fragile X syndrome explore a range of psychosocial aspects in addition to looking at uptake of testing and mutation frequency. Genet Med 2010:12(7):396 -410.Key Words: attitudes, carrier screening, fragile X syndrome, newborn screening, psychosocial P opulation-based screening programs for a number of genetic conditions have been established in newborn, prenatal, and preconception settings. Specific criteria, such as those developed by the World Health Organization, 1,2 are available to provide guidance on which conditions are suitable for screening. 3 Fragile X syndrome (FXS) is an X-linked genetic condition for which possible inclusion in population-based screening programs has been discussed and debated for many years. 4 -7 FXS is the most common known cause of inherited intellectual and developmental disability. It has a serious adverse impact on individuals and their families that is equivalent to that of other disabilities such as Down syndrome and autism. Most FXS cases are caused by the silencing of the FMR1 gene, which is located on the X chromosome. In these cases, the FMR1 gene is switched off as a result of an increase in the number of hypermethylated trinucleotide (CGG) repeats in the 5Ј untranslated region of the gene. Current definitions describe the normal range of CGG repeats as 6 -44, the "gray zone" range as 45-54 repeats, and the premutation range as 55-199 repeats. 8 Those affected by FXS have Ͼ200 repeats (full mutation). The length of the CGG repeat is unstable over a certain size, such that a premutation can expand to a full mutation when passed onto offspring through female, but not male, premutation carriers. 9 -11 Similarly, a gray zone allele can increase to a premutation allele when transmitted to offspring, such that a grandchild could be affected with FXS.The full mutation is associated with intell...