Oxidative stress represents a deregulation of the homeostasis between the reactive oxygen species and the mechanisms of detoxification and repair. By analyzing the level of oxidatively damaged DNA bases and nucleosides in urine we can assess the extent of DNA repair within the whole body. High levels of markers of oxidative DNA damage excreted in the urine indicate elevated levels of oxidative stress, but can also reflect a high level of efficiency of the processes that work to repair this damage (oxidative stress can be high and the repair processes eliminate its effects). In the present review we discuss the role of oxidative stress, oxidative DNA damage repair mechanisms, potential sources of 8-oxoGua and 8-oxodG (basic markers of oxidative stress) content in urine, effect of antioxidant supplementation on the levels of oxidative DNA lesions, potential application of oxidative DNA damage determination in clinical practice.