Werner syndrome (WRN) is a rare autosomal recessive disorder, one of the progeroid syndromes, and is characterized by features of premature aging. The incidence of WRN in the Japanese population, 1 in 200,000, is higher than than that in the Caucasian population. The genetic defect of WRN is unknown. But genetic linkage to several markers on the short arm of chromosome 8 has been reported recently. Here, we studied one family with WRN in which an affected individual had a papillary thyroid carcinoma and myelodysplastic syndrome. Using 4 microsatellites closely located to the WRN locus: D8S360, D8S1055, D8S339 and ANK1, we analyzed the genotypes of this patient, her three siblings and her parents, who were first cousins. The mutative haplotype, identified through the generations in pedigree, helps detect a carrier or a presymptomatic patient. The eldest sister inherited two normal haplotypes, but the second sister inherited one mutative haplotype. There was no difference in clinical signs and symptoms between these sisters. when the WRN gene is isolated, it will help us understand the mechanism of aging.