Background:There is an increase of risk of coronary artery disease about 4-fold with diabetes mellitus, and ischemic heart disease is liable for diabetes-related deaths. In this study, we examined the association between glycemic control, as determined by Hemoglobin A1c, and the incidence of periprocedural complications in diabetic patients who had coronary artery bypass graft (CABG) undergoing percutaneous coronary intervention (PCI). Aim of the study:To assess the effect of control of DM on the outcome of PCI in patients who underwent CABG. Methods:This comparative cross-sectional study was conducted at the department of cardiology in Zagazig university hospital included all 24 patients with CABG & DM during the period from January 2019 to January 2020 divided into controlled DM (HbA1c>7)&12 patients with uncontrolled DM (HbA1c<7)comparative control group. All patients were subjected to full medical history, complete clinical examination, Pre-operative Laboratory Workup: Kidney function, Complete blood counts, and Glycosylated Hemoglobin HbA1c as a marker for control of DM, ECG, and ECHO. Results:There was no statistically significant difference between both groups in-hospital stay (p= 0.131), but there was a statistically higher significant increase in periprocedural complications in uncontrolled DM compared to controlled DM. There was a statistically significant negative correlation between control of DM and periprocedural complications in both groups (p=0.028). Conclusion:control of DM guided by HbA1c level (<7) reduces the complications during percutaneous coronary intervention in diabetic patients with a previous coronary artery bypass graft. And in these patients who need elective PCI, control of their diabetes is advised before the procedure.