The implication of DNA hypermethylation in the pathogenesis of myelodysplastic syndromes (MDS) provides a rationale for using hypomethylating agents such as azacitidine. Growing evidence suggests that azacitidine may reverse epigenetic gene silencing at specific genomic targets. AZA-001 established azacitidine as the first agent to provide a significant overall survival benefit in MDS patients. These data confirmed that azacitidine has a progressively cumulative effect on the MDS clone and support the value of maintenance therapy. Prolonged survival was independent of achieving complete response. Azacitidine in combination with histone deacetylase inhibitors might offer better efficacy by modulating the methylation and acetylation states of silenced genes.