Summary Metabolic syndrome represents a collection of cardiovascular risk factors, including overweight, hypertension, dyslipidemia and impaired glucose metabolism, with insulin resistance. In recent years, the potential relationship between metabolic syndrome and male factor infertility has been studied. As endothelial dysfunction is the hallmark of metabolic syndrome, the aim of this work was to assess serum levels of YKL-40 as a marker of endothelial dysfunction in male patients with idiopathic infertility. The study revealed that YKL-40 levels were elevated in patients than controls denoting that endothelial dysfunction might play a role in the pathogenesis of idiopathic infertility and that YKL-40 as a marker of endothelial dysfunction could be a useful marker of idiopathic infertility.