Aim: Aberrant DNA methylation patterns are a hallmark of cancer, although the extent to which they underlie cancer development is unknown. In this study, we aimed to determine whether acute lymphoblastic leukemia (ALL) patients in clinical remission retained abnormal DNA methylation patters and whether these were associated with patient outcome. Materials & methods: We investigated CpG island methylation of genes known to exhibit hypermethylation in leukemia using quantitative pyrosequencing analysis. Results: Although methylation levels were reduced in remission samples, they remained significantly higher than those seen in healthy controls. This retained methylation was not related to low levels of residual leukemia cells still present at remission. Methylation levels were also stable (or increased) during continuous remission and significantly correlated with long-term survival in adult ALL patients. Conclusion: This study determined that abnormalities in DNA methylation are retained during ALL remission and may represent a novel prognostic marker for adult ALL patients.