Myelodysplastic syndrome is a clonal bone marrow stem cell disorder characterized by a decrease in blood cells due to ineffective hematopoiesis, progressing to acute myeloid leukemia in one third of patients and occurring in 15% of cases following cancer prior to treatment with chemotherapy or radiation therapy; this syndrome is common in the elderly. Its pathophysiology includes cytogenetic alterations with or without gene mutations, and gene methylation usually occurs in advanced stages. Clinical manifestations caused by hemocytopenia include anemia, infections and bleeding. Diagnosis is made on the basis of blood and bone marrow tests, which show hematocrit and an excess of bone marrow cells, sometimes accompanied by an excess of primitive cells. The prognosis depends largely on the proportion of primitive cells in the bone marrow, the amount and extent of hematocrit and cytogenetic abnormalities. Treatment of patients with low-risk myelodysplastic syndromes, particularly for anemia, includes growth factors, lenalidomide and blood transfusions. Treatment for higher-risk patients includes demethylating drugs and, if possible, allogeneic stem cell transplantation. Incidence and etiology] Myelodysplastic syndromes often occur in older patients, with a median age at diagnosis of 65-70 years; <10% of patients are younger than 50 years. Myelodysplastic syndromes occur mostly in men, except for an isolated 5q deletion that occurs mainly in women. The annual incidence of myelodysplastic syndromes is approximately 4 >70 years of age reaching 40-50/100,000 patients). To the best of our knowledge, there are no racial differences in incidence; however, the syndrome occurs at an earlier age in Asian populations relative to Western populations, with a greater likelihood of cytopenic bone marrow and an uncommon isolated 5q deletion. Only 15% of patients with myelodysplastic syndromes are known to have a cause (Figure). A hereditary predisposition is more pronounced in one-third of pediatric patients, including pediatric patients with Down syndrome, Fanconi’s anemia, and multiple neurofibromas. Genetic predisposition is less common in adult patients, but should be studied in adolescents or other family members with myelodysplastic syndromes, acute myeloid leukemia, or aplastic anemia. Environmental factors include prior use of chemotherapies, especially alkylating agents and purine analogs, radiation therapy and smoking. Occupational factors include exposure to benzene and its derivatives, with a higher incidence in workers in agriculture and industry. Those patients with secondary myelodysplastic syndromes, especially cases occurring after receiving chemotherapy, usually have a poor prognosis with complex cytogenetic findings.