Purpose of the study was to investigate the value of serum gamma glutamyltransferase (GGT) activity as a cardiovascular risk factor in a population sample of 868 men and women among the cohort of the Turkish Adult Risk Factor Study, surveyed in 2003. Metabolic syndrome (MS) was diagnosed based on criteria of the ATP-III, and coronary heart disease (CHD) on the presence of angina and Minnesota coding of the resting ECGs. MS was observed in 37%, CHD in 10.5% of the study sample. GGT activity was measured by the Elecsys method, and values were log-transformed due to the skewed distribution. In 421 men and 447 women (mean age 52.7±11 years), geometric means of GGT were 28.7±1.8 U/L and 20.8±1.8 U/L, respectively (p<0.001). Concentrations rose mildly with age (r =0.11). Strongest correlations existed with serum uric acid, fasting triglycerides and insulin, complement C3, waist circumference and with the diagnosis of metabolic syndrome (r = 0.3 to 0.4). Moreover, significant correlations were found between GGT and BMI, total cholesterol and physical inactivity in both genders, and systolic pressure and impaired fasting glucose (r 0.16 to 0.25) in women alone. Alcohol intake and waist circumference, followed by body mass index, levels of uric acid, fasting insulin and complement C3 were the significant independent determinants of serum GGT activity among 13 variables included in a multiple linear regression analysis. A 2-fold increase in serum GGT levels was associated by logistic regression analysis with a rise of 36% in MS likelihood - independent of age and sex (p<0.001). Optimal cutoff points of GGT for CHD likelihood were selected as 50 U/L and 35 U/L in men and women, respectively. As opposed to individuals below the cutoff, those above the cutoff exhibited an odds ratio for CHD likelihood of 2.17 (95%CI 1.23; 3.82) - independent of age, sex and alcohol usage - indicating that, a 2-fold elevation in serum GGT activity corresponded to a 58% excess in CHD likelihood. This population-based study among Turkish adults confirmed that serum GGT activity is closely linked to the metabolic syndrome and its components. GGT proved to be a good marker of CHD likelihood, and moderate elevations of its activity significantly reflected a rise in this likelihood. Cutoff values suitable for use in clinical practice were proposed.