The authors hypothesized that matrix metalloproteinase (MMP)-2, -9, and tissue inhibitor metalloproteinase (TIMP)-1, -2 would be abnormal in acute coronary syndromes (ACSs). MMP-2, -9, and TIMP-1, -2 plasma levels were measured in diabetic patients with ACSs compared to nondiabetic patients with ACSs. A total of 46 diabetic and 78 nondiabetic patients with ACSs were enrolled. The following parameters were measured: body mass index (BMI), glycosylated hemoglobin (HbA1c), fasting plasma glucose (FPG), fasting plasma insulin (FPI), homeostasis model assessment index (HOMA index), systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (Tg), lipoprotein(a) [Lp(a)], plasminogen activator inhibitor-1 (PAI-1), homocysteine (Hct), fibrinogen (Fg), high-sensitivity C-reactive protein (hs-CRP), and plasma levels of MMP-2, MMP-9, TIMP-1, and TIMP-2. Significant HbA1c, FPG, FPI, HOMA index, DBP, Tg, Hct, and Fg increases were present in the diabetic group with ACSs, whereas hs-CRP was lower in these patients compared to nondiabetic patients with ACSs. MMP-9, TIMP-1, and TIMP-2 plasma levels were higher in diabetic patients with ACSs compared to nondiabetic patients with ACSs. MMP-9, TIMP-1, and TIMP-2 plasma levels were increased in diabetic patients with ACSs, which may reflect abnormal extracellular matrix metabolism in diabetes during acute event.