Aberrant hypermethylation of promoter regions in specific genes is a key event in the formation and progression of cancer. In at least some situations, these aberrant alterations occur early in the formation of malignancy and appear to be tumour specific. Multiple reports have suggested that measurement of the methylation status of the promoter regions of specific genes can aid early detection of cancer, determine prognosis and predict therapy responses. Promising DNA methylation biomarkers include the use of methylated GSTP1 for aiding the early diagnosis of prostate cancer, methylated PITX2 for predicting outcome in lymph node-negative breast cancer patients and methylated MGMT in predicting benefit from alkylating agents in patients with glioblastomas. However, prior to clinical utilisation, these findings require validation in prospective clinical studies. Furthermore, assays for measuring gene methylation need to be standardised, simplified and evaluated in external quality assurance programmes. It is concluded that methylated genes have the potential to provide a new generation of cancer biomarkers. ; Keywords: Breast Neoplasms; CpG Islands; DNA Methylation; DNA, Neoplasm; Disease Progression; Female; Gene Expression Regulation, Neoplastic; Genetic Markers; Glioblastoma; Humans; Lung Neoplasms; Male; Neoplasm Proteins; Neoplasms; Ovarian Neoplasms; Precancerous Conditions; Promoter Regions, Genetic; Prostatic Neoplasms; Tumor Markers, Biological