Deletions of Xq are extremely rare events in myelodysplastic syndromes (MDS) patients and were previously described in five patients, in two of them as a sole chromosome abnormality. We found isolated del(Xq) in 3 of 127 MDS patients with clonal chromosome changes. Detailed analysis of clinical and morphological data of presented and previously published cases indicates the following: (1) del(X)(q24) and del(X)(q13) are nonrandom chromosomal abnormalities in MDS; (2) MDS with deletions of Xq affect exclusively females ages 46-65; and (3) deletions of Xq are associated with refractory anemia with excess blasts (RAEB) and indicate an unfavorable prognosis.