Urinary levels of the RNA oxidation marker 8-oxo-7,8-dihydroguanosine (8-oxoGuo) measured in 1,381 patients newly diagnosed as having type 2 diabetes mellitus predicted mortality after a median follow-up period of 18.7 years. The hazard ratios for patients in the highest 8-oxoGuo quartile compared with patients in the lowest quartile were 1.44 (1.12–1.85) for all-cause mortality and 1.54 (1.13–2.10) for diabetes-related mortality. No relationship was found between urinary levels of a marker of DNA oxidation and mortality in this population.