Background: Remnant cholesterol (RC) is receiving increasing attention regarding its relation to cardiovascular risk. Whether RC is associated with periprocedural myocardial injury (PMI) following percutaneous coronary intervention (PCI) in type 2 diabetes (T2D) is currently unknown. Methods: We prospectively enrolled 1182 consecutive T2D patients who were scheduled for PCI but with baseline normal preprocedural cardiac troponin I (cTnI). Patients were divided according to their glycemic control status: group A [glycated hemoglobin (HbA1 c) < 7%, n 563]and group B (HbA1c > 7%, n = 619). PMI was evaluated by cTnI analysis within 24 h. The associations of preprocedural RC and the RC to high-density lipoprotein cholesterol ratio (RC/HDL-C) with PMI were investigated. Results: The associations of RC and RC/FIDL-C with PMI were observed in group B (both p < 0.05) but not in group A (both p > 0.05). Patients in group B, a 1-SD increase of RC produced 30% and 32% increased risk for postprocedural cTnl > 3x upper limit of normal (ULN) and >5 x ULN, respectively. The odds ratios for RC/FIDL-C were the highest compared with any cholesterol fractions including total cholesterol (TC)/HDL-C, low density lipoprotein cholesterol (LDL-C)/HDL-C, nonHDL-C/HDL-C, and triglyceride/HDL-C with 1.43 [95% confidence interval (CI): 1.10-1.88] for >3x ULN and 1.49 (95% CI: 1.13-1.97) for >5x ULN. However, no such associations were found in group A. Furthermore, patients with RC >27.46 mg/dL (third tertile) [RC <= 14.15 mg/dL (first tertile) as reference] were associated with a 1.57-fold and 2-fold increased risk for >3x ULN and >5x ULN in group B, respectively. Conclusions: RC and RC/HDL-C might be valuable, independent predictors for PMI in poorly-controlled diabetic patients undergoing PCI. (C) 2017 Published by Elsevier Ltd on behalf of Japanese College of Cardiology.