A case of mosaic Turner's syndrome with a 45,X/46,XX/47,XXX karyotype, who was 
also a fragile X obligate carrier as the mother of an affected boy, was 
identified by molecular diagnosis. Complete haplotyping and direct DNA analysis 
showed that the X chromosome in all metaphases was the normal X. At the age of 
57, she is mentally normal. Her external appearance was typical of Turner's 
syndrome. This report shows that molecular studies in conjunction with 
cytogenetic analysis can help in the clinical diagnosis of a rare case and can 
show the uniqueness of a case such as the one here described.