Objective: To evaluate endothelial progenitor cells (EPCs) and systemic microvascular function in patients with severe hypercholesterolemia, comparing patients with the definite familial hypercholesterolemia (FH) phenotype (DFH) or probable/possible FH phenotype (PFH). There is a large spectrum of atherosclerotic disease between these two clinical phenotypes of FH, and to acquire further knowledge of the pathophysiology of vascular disease in both is desirable. Methods: Subjects with severe hypercholesterolemia, defined as low-density lipoprotein cholesterol (LDL-C) >190 mg/dL, were classified as DFH or PFH and underwent measurement of the number of EPCs by flow cytometry and evaluation of cutaneous microvascular reactivity using a laser speckle contrast-imaging system with iontophoresis of acethylcholine (ACh) or sodium nitroprusside. EPCs were defined as CD45- or CD45low, CD34+CD133+CD309+ cells. Categorical variables were compared using Fisher test and continuous variables with Student t test or Mann-Whitney test, and a value of p < 0.05 was considered statistically significant. Results: Patients with DFH had higher LDL-C than those with PFH. There was no difference in the median number of EPCs between patients with DFH or PFH, but there was a significant reduction of endothelial-dependent, ACh-induced vasodilatation in the former. Conclusion: Patients with DFH have impaired microvascular endothelial-dependent vasodilatation compared to those with PFH, indicating more severe vascular disease in the former.