Telomeres are the repeat DNA sequences at the end of chromosomes necessary for successful DNA replication and chromosomal integrity. Telomeres shorten at cell division at a rate determined by oxidative DNA damage, and cells are triggered into replicative senescence once telomeres shorten to a critical length. Telomere-related chromosomal maintenance also has a role in carcinogenesis. Type 2 diabetes is characterised by increased oxidative stress, increased oxidative DNA damage, senescent retinal and renal phenotypes, and an increased risk of epithelial malignancy. We suggest that increased oxidative DNA damage and telomere attrition in type 2 diabetes leads to: (1) carcinogenic telomere-dependent chromosomal non-reciprocal translocations, genomic instability, and the development of epithelial cancers; (2) senescent retinal and renal phenotypes (expressed as diabetic retinopathy and nephropathy); and (3) senescent vascular endothelial, monocyte-macrophage and vascular smooth muscle cells (expressed as endothelial dysfunction and accelerated atherogenesis). An adverse intrauterine environment leads to increased feto-placental oxidative stress and feto-placental oxidative DNA damage. We also suggest that intrauterine oxidative DNA damage and telomere shortening is another point at which increased oxidative stress could contribute to a pre-programmed increased risk of senescent phenotypes in adult offspring, characterised by type 2 diabetes and epithelial malignancy. These suggestions can be used to understand early glucose intolerance in the young children of type 1 diabetes pregnancies, poor cancer outcomes in type 2 diabetes, beta cell fatigue in type 2 diabetes and the absence of increased epithelial cancer risk in type 1 diabetes.