DNA methylation is the best known and most thoroughly studied epigenetic mechanism. Hypermethylation of CpG islands associated with silencing of tumour suppressor genes or tumour-related genes is a common hallmark of human cancer. The list of tumour-related genes with aberrant hypermethylation in their CpG islands has been increasing. There is also the potential for using DNA methylation profile data as markers for various types of human cancer. In this paper, we review the methylation profile of testicular germ cell tumours (TGCTs). We show that TGCTs have distinctive DNA methylation profiles that differ from those of somatic tissue-derived cancers or somatic tissues. We also discuss the methylation profile of TGCTs in terms of the DNA reprogramming that occurs in primordial germ cells or pre-implantation embryos. Finally, we describe the potential clinical utility of this unique methylation phenotype in TGCTs with regard to developing a novel tumour marker. These data suggest that unmethylated DNA fragments in TGCTs may have diagnostic implications. Further elucidation of epigenetic profiles in TGCTs is expected to provide a new insight into the biology of this disease.