Background- Patients undergoing non-cardiac vascular surgery are in danger of a MACE (major adverse cardiovascular event), and biomarkers are needed for surgical risk prediction. We hypothesised that oxidative stress occurring during surgery may lead to LDL oxidation. Furthermore, as oxLDL (oxidised Low-density Lipoprotein) has been implicated in atheromatous plaque instability, increased levels of oxLDL may be associated with perioperative MACE. Methods- Plasma oxLDL recognised by the in-house generated mAb LO1 was measured by a capture ELISA in samples taken 12-24 hours before non-cardiac vascular surgery (baseline), and 24 hours and 72 hours post-surgery. We also used a capture ELISA to measure Apolipoprotein B (ApoB), enabling adjustment of oxLDL for LDL level changes. Study endpoints were in-patient MACE. Values are expressed in arbitrary units as median,{interquartile range}, compared by Wilcoxon matched-pairs signed rank test for paired data and Mann-Whitney test for unpaired data. Receiver Operator Curves were used to plot the trade-off of sensitivity and specificity of biomarkers and risk scores in predicting outcomes. Statistical significance was defined as a p-value <0.05. Results- oxLDL levels adjusted to ApoB (oxLDL/ApoB) were significantly increased between baseline and 24 hours (0.0029,{0.0018,0.0044} vs 0.0034 {0.0023,0.0051}, p<0.0001) and then decreased at 72 hours (0.0028,{0.0018,0.0041}, p<0.0001) back to baseline levels (n=131 patients). MACE occurred in 25/131, and these were not predicted by baseline oxLDL/ApoB levels (AUC=0.5377, p=0.5581). However, patients with a post-operative MACE had a significantly larger increase in oxLDL/ApoB levels between baseline and 24 hours post-surgery (0.00082, {-0.000029, 0.0016} vs 0.00026 {-0.00041, 0.00092}, p=0.0238). Conclusion- Our study provides evidence for an increase in plasma oxLDL during the course of vascular surgery, an effect that could not be explained by perioperative changes in LDL. The significant link between large increases in oxLDL levels and MACE may indicate that those with greater operative oxidative stress are more likely to develop a MACE. Alternatively, perioperative MACE may add to oxidative stress. Regardless, oxLDL levels may be worth measuring as a surrogate marker of impending cardiovascular complications following vascular surgery.