Structural anomalies of the X chromosome, especially translocations, are rare events in myelodysplastic syndromes (MDS). In a series of 2270 MDS patients analyzed between 1983 and 1994 (Center for Human Genetics, Leuven), 9 cases were found with translocations involving the X chromosome. These aberrations were not restricted to specific FAB subtypes and were the sole anomalies in 3 cases. In the remaining 6 patients, they were associated with other abnormalities, including 5q-, observed in three cases. Fluorescence in situ hybridization (FISH) was retrospectively performed on 8 patients and was shown to be a useful complement for the characterization of the translocations involving the X chromosome. In 3 cases, we could identify translocation partners and breakpoint regions only by using chromosome painting. No recurrent chromosome partners were observed. The breakpoints could be localized along the whole X chromosome. There was, however, a cluster in the Xq13 region involved in 4 of the 9 patients. The previously reported association of Xq13 anomalies with refractory anemia with ringed sideroblasts (RARS) was found in only one case. Despite the lack of characteristic translocations involving the X chromosome, the occurrence of such changes as the sole karyotypic anomaly suggests that they could play a role in the pathogenesis of some myelodysplastic syndromes.