In vitro studies attribute antiatherogenic and insulin-like properties to zinc (Zn). However, only a few conflicting clinical data exist concerning the relationship between Zn and coronary artery disease (CAD) as well as glycemic indices. We studied 72 patients without prior history of myocardial infarction or revascularization procedures, who underwent coronary angiography for evaluation of chest pain. Coronary artery disease severity was estimated using 3 angiographic scores. Zn in serum and 24-hour urine, as well as serum Zn/24-hour urine Zn ratio were determined. Serum Zn was not associated with CAD prevalence and severity. However, urinary Zn loss was significantly higher among patients with CAD and showed a positive association with CAD severity. Serum Zn/24-hour urine Zn ratio was inversely associated with CAD, as well as with diabetes mellitus prevalence, fasting glucose, and glycated hemoglobin levels. Low serum Zn/24-hour urine Zn ratio is associated with angiographically severe atherosclerosis and impaired glucose homeostasis.