Psoriasis is a disease that can contribute to a risk of atherosclerosis. In several studies, impaired endothelial dysfunction (ED) is correlated with psoriasis. Serum YKL-40 is a new inflammatory biomarker of vascular damage, like ED and cardiovascular diseases. The aim of the study was to compare relevance of serum YKL-40 levels in psoriasis patients and healthy subjects according to ED diagnosis and identifiable cardiovascular risk factors. Sixty (31 female, 29 male) patients with plaque psoriasis, and 30 (18 female, 12 male) healthy controls were selected according to whether they had at least one or no identifiable risk factors for cardiovascular disease. All subjects were evaluated ultrasonographically for endothelial function and diagnosed as with or without ED and all groups compared for serum YKL-40 levels. YKL-40 levels of psoriatic patients with ED were higher than healthy controls with ED (P = < 0.05). There were no statistical differences in between subjects without ED. YKL-40 levels of patients over age of 40 were higher than younger ones (P < 0.05). But in healthy controls, there were no differences. In comparison of cardiovascular risk-positive (RP) patients and RP healthy subjects, YKL-40 levels were higher in RP patients (P = < 0.05). The elevation of plasma YKL-40 in psoriasis can be associated not only with inflammation of the disease, but also with ED. YKL-40 can be used as a marker for predicting and preventing cardiovascular diseases in RP psoriatic patients with age above 40.