Aberrant DNA methylation is one of the molecular hallmarks of cancer and leukemia. By repressing gene expression, it is considered a functional equivalent to the physical inactivation of tumor suppressor genes by deletions or mutations. To clinically exploit this process, compounds with DNA hypomethylating properties have been evaluated both in the laboratory and the clinic. Two such agents, 5-azacytidine and 5-aza-2'-deoxycytidine, are currently approved by the US Food and Drug Administration for the treatment of patients with myelodysplastic syndromes. Ongoing studies are evaluating alternative dosing schedules for these drugs and the activity and safety of this class of agent in combination with histone deacetylase inhibitors. Here we summarize the experience of hypomethylating agents in myelodysplastic syndromes.