Objective: This study illustrates the relationship between oxidative DNA damage andobesity in patients with prediabetes and type 2 diabetes compared to controls.Design &Methods: Participants attended the School of Community Health, Diabetes Screening Clinic, Charles Sturt University, Australia between February 2006 & June 2008.One hundred and sixty two participants (35 type 2 diabetic patients; 8 prediabetes and 119age, gender and weight matched controls) were investigated. All patients were selected on clinical grounds.Results: Serum 8-hydroxy-2-deoxy-guanosine (8-OHdG) level was significantly greater in the prediabetes (671.3 ± 140 pg/ml) compared to controls (210.1±166 pg/ml; p<0.01). The diabetes group (1979.6±1209 pg/ml) had the highest level of 8-OHdG. There was a significant increase in serum 8-OHdG in obese subjects (848.5±103 pg/ml, p<0.001) and overweight subjects (724±102 pg/ml, p=0.005) compared to the lean subjects (196.5±327pg/ml).Conclusion: Our results indicate that serum 8-OHdG is increased already in prediabetes suggesting oxidative DNA damage to be present with minor elevation of blood glucoselevels. The statistical significant positive correlation between serum 8-OHdG and body mass index in the diabetic group indicates that obesity has an additive effect to increased blood glucose level contributing to oxidative DNA damage.