Elevated gamma-glutamyltransferase (GGT) level is independently correlated with conditions associated with increased atherosclerosis, such as obesity, elevated serum cholesterol, high blood pressure and myocardial infarction. It is demonstrated that serum GGT activity is an independent risk factor for myocardial infarction and cardiac death in patients with coronary artery disease. Diabetes is also a well-known cardiovascular risk factor and an equivalent of coronary artery disease. Although the relationship between GGT and coronary artery disease has been reported, there are limited data exploring the changes of GGT in acute coronary syndromes, especially in patients with diabetes. So, this study aimed to determine changes in GGT level in diabetic and non-diabetic acute coronary syndromes. This trial was carried out at Kosuyolu Cardiovascular Training and Research Hospital and Van Yuksek Ihtisas Hospital, Turkey. A total of 219 patients (177 men and 42 women) presenting with acute coronary syndrome) and 51 control subjects between September 2007 and September 2008 were included in the study. Serum gamma-glutamyltransferase and serum lipoprotein levels were determined. The resuls indicated that serum GGT levels were higher in acute coronary syndrome patients compared with control. In subgroup analyses, there was no difference between diabetic and non-diabetic subgroups. There was also weak correlation between GGT and blood glucose levels. There was no correlation between GGT and serum lipoprotein levels. In conclusion, serum GGT levels were higher in acute coronary syndrome patients. In subgroup analyses, There was no difference between diabetic and non diabetic subgroup.