Epigenetic alterations play a major role in cancer. Recently we reported that stem cell Polycomb group targets (PcGTs) are up to 12-fold more likely to have cancer-specific promoter DNA hypermethylation than nontargets. To identify potential, prognostic DNA methylation markers in ovarian cancer we analyzed the DNA methylation at 71 different loci in 22 ovarian cancers and 18 non-neoplastic ovarian specimens by means of a quantitative, real-time PCR-based technique (MethyLight). We identified DNA methylation of HOXA10 and HOXA11, both of them PcGTs, to be the best discriminators between cancer and non-neoplastic tissue. In an independent set consisting of 92 ovarian cancer specimens further analysis demonstrated that HOXA11 DNA methylation is (i) strongly associated with the residual tumor after cytoreductive surgery and (ii) is a marker indicating poor prognosis. HOXA11 DNA methylation was independently associated with poor outcome [relative risk for death 3.4 (95% CI 1.2-9.9; p = 0.03)]. These findings support the view that the technical inability to optimally cytoreduce ovarian cancer is associated with particular molecular alterations in the tumor which per se define a subgroup of patients with poor outcome.