Prediabetes is a disorder of glucose metabolism that reflects the natural history of progression from normoglycaemia to type 2 diabetes mellitus. Patients with prediabetes have impaired glucose regulation caused by insulin resistance (IR). IR in patients undergoing percutaneous coronary intervention (PCI) is associated with coronary artery remodeling and coronary plaque vulnerability by intravascular ultrasound (IVUS) analysis. In stent restenosis after bare metal and drug-eluting stent implantation more frequently is observed in patients with high fasting-insulin levels and IR. Although IR has a significant role in the progression of atherosclerosis in prediabetic patients, the importance of managing prediabetes is often under-appreciated by clinicians. To date, no pharmacological treatment has been officially approved for prediabetes. According to American Diabetes Association recommendations, metformin is the only drug that could be considered in the treatment of prediabetic patients with a high risk of developing diabetes. Metformin is a safe and inexpensive glucose lowering drug that attenuates mortality and future cardiovascular events in patients with type 2 diabetes as well as the progression of atherosclerosis in non-diabetic animal models. This study was designed to analyze coronary plaque characteristics by iMAP IVUS in patients with and without prediabetes undergoing PCI and to evaluate the impact of metformin treatment on coronary plaque characteristics in prediabetic patients at 24 month follow up.