OBJECTIVE: Familial Mediterranean Fever is an autoinflammatory disease characterized by inflammatory attacks in serous tissues often accompanied by endothelial dysfunction. This study aimed to evaluate the effect of endothelium-derived hyperpolarizing factor, which is an indicator of endothelial dysfunction in children with familial Mediterranean fever. METHODS: This study include 57 children with familial Mediterranean fever and 31 children as healthy controls. Blood samples were collected from all participants to measure their endothelium-derived hyperpolarizing factor, complete blood count and C-reactive protein. In addition, inflammatory markers, mutation analyses, and microalbuminuria were examined only in the patient group. RESULTS: The mean age of the patient group was 9.8 ± 4.0 (2.5-18) years, while the mean age of control group was 9.5 ± 3.9 (2.5-16) years (p=0.808). Study group had significantly higher C-reactive protein levels and systolic and diastolic blood pressures and lower endothelium-derived hyperpolarizing factor values than the control group (p=0.0001, p=0.002, p=0.035 and p=0.009, respectively). CONCLUSION: Low levels of endothelium-derived hyperpolarizing factor, high levels C-reactive protein and high blood pressure in patients with familial Mediterranean fever can be attributed to the changes in the endothelium resulting from subacute inflammation.