Oxidative stress to DNA from smoking was investigated in one randomized smoking cessation study and in 36 cohort studies from excretion of urinary 8-oxo-7-hydrodeoxyguanosine (8-oxodG). Meta-analysis of the 36 cohort studies showed smoking associated with a 15.7% (95% CL 11.0:20.3, p < 0.0001) increased oxidative stress to DNA, in agreement with the reduction of oxidative stress to DNA found in the smoking cessation study. Meta-analysis of the 22 studies that used chromatography methodology on 1709 persons showed a significant 29.3% increase in smokers (95% CL 17.3;41.3), but meta-analysis of 14 studies on 3668 persons using ELISA methodology showed a non-significant effect of 8.7% [95% CL -1.2;18.6]. Tobacco smoke induces oxidative damage to DNA; however, this is not detected with ELISA methodology. Currently, the use of existing ELISA methodology to measure urinary excretion of 8-oxo-7-hydrodeoxyguanosine cannot be recommended.