Endocan is a soluble proteoglycan, secreted by human vascular endothelial cells. Endocan is a marker for vascular pathologies and an important mediator of angiogenesis, strongly associated with inflammation, vascular endothelial dysfunction, and atherosclerosis. The relationship between coronary artery ectasia (CAE) and endocan has not been evaluated. We aimed to investigate this association. Fifty-four patients with isolated CAE without coronary stenosis and 30 controls with normal coronary angiogram were included in this study. Endocan plasma concentrations were measured using an enzyme-linked immunosorbent assay. Patients with isolated CAE had significantly higher levels of endocan compared to the controls (18.9 ± 7.3 vs 15.6 ± 3.6 ng/mL; P = .007). There was a significant correlation between endocan levels and severity of isolated CAE according to the Markis classification (r = −.593, P < .001). Plasma endocan levels may reflect the presence and severity of isolated CAE, suggesting that endocan may be involved in pathogenesis of isolated CAE.