Background: Conventional risk factors including smoking have been known to be important factors of coronary artery spasm (CAS). But there are few reports showing relationship between CAS and the risk factors in younger people. Methods: The study consisted of 199 younger patients (���45 years old) without significant coronary artery stenosis. We underwent Ach provocation test by injecting incremental doses of 20, 50 and 100 g to left coronary artery. Significant coronary artery endothelial dysfunction was defined as focal or diffuse severe transient luminal narrowing (>70%). The impact of patient���s conventional risk factors and biochemical markers on Ach-induced coronary artery endothelial dysfunction was analyzed. Results: Forty percent of enrolled patients showed positive Ach provocation test (79/199). The mean age was significantly higher and hypertension was tend to be higher in provocation (+) group. There were no significant differences in the rate of other conventional risk factors (diabetes, hyperlipidemia and smoking) and the level of Total Cholesterol, Triglyceride, HDL-cholesterol, HbA1c, hs-CRP and ESR. But the level of LDL-cholesterol was significantly higher in provocation (+) group (Table). Conclusions: The higher level of LDL-cholesterol has the possibility of strong relationship with the worsening of Ach-induced coronary endothelial dysfunction in younger patients.