It has been recognized that some patients with myelodysplastic syndromes (MDS) develop immunologic abnormalities, but little is known of its correlations to MDS-specific disease features. In a retrospective study of 284 MDS patients, we identified 32 patients (11.3%) with clinical or serologic immunological abnormalities (group A) and compared them to the remaining 252 cases (group B). Group A consisted of 20 patients with clinical signs of autoimmune disease and 12 asymptomatic patients with serologic immunological abnormalities only. Apart from significant female predominance in group A (M/F = 2.5 vs M/F = 0.7, p = 0.001), the other clinical and biological features such as median age, distribution of MDS subtypes, incidence of karyotyopic abnormalities, "abnormal" in vitro growth of GM-progenitors and survival times were similar in the two groups. Autoimmune manifestations partially responded to immunosuppressive therapy, with moderate improvement of peripheral cytopenia. In addition, CD3(+), CD4(+), CD8(+), CD19(+), and CD56(+) cells were quantified in peripheral blood of 38 patients. Matched with similarly aged healthy control group, most MDS patients showed significant lymphocytopenia, mainly due to the reduction of T-helper series (in both absolute numbers and percentage). B-cells were reduced in absolute numbers, but their percentage still overlapped with the control. No major abnormalities of natural killer cells (CD56(+)) were seen. We conclude that autoimmune diseases and asymptomatic immunologic abnormalities are common in patients with MDS, but except for female predominance, no correlation between these abnormalities and MDS-specific disease features were found.