OBJECTIVE: Increased wall-to-lumen ratio of small arteries is a predictor of adverse cardiovascular prognosis. We aimed to analyze retinal arteriolar structure in never-treated patients with essential hypertension and to test whether elevated blood pressure is associated with an increased wall-to-lumen ratio of retinal arterioles. METHODS: The study cohort comprised 21 untreated male patients with essential hypertension (mean age 39.1 ± 5.4 years) and 29 untreated normotensive men (mean age 36.7 ± 5.9 years). Wall-to-lumen ratio of retinal arterioles was assessed in vivo using scanning laser Doppler flowmetry. RESULTS: Patients with essential hypertension had a higher wall-to-lumen ratio of retinal arterioles than normotensive individuals (0.36 ± 0.1 vs. 0.28 ± 0.1, P = 0.028). Wall cross-sectional area of retinal arterioles did not differ between the study groups. The growth index, indicating the percentage of difference in average wall cross-sectional area of retinal arterioles between both groups, was 18%. Both systolic (r = 0.360, P = 0.010) and diastolic (r = 0.536, P < 0.001) blood pressures were related to wall-to-lumen ratio of retinal arterioles. Multiple regression analysis including a variety of known cardiovascular risk factors revealed that blood pressure is independently associated with an increased wall-to-lumen ratio of retinal arterioles (systolic blood pressure: β = 0.417, P = 0.012; diastolic blood pressure: β = 0.548, P = 0.001). CONCLUSION: The changes in arteriolar structure of retinal vessels in our study cohort revealed a similar pattern to that observed previously by other investigators in subcutaneous small arteries in essential hypertension. Blood pressure emerged as an important and independent determinant of wall-to-lumen ratio of retinal arterioles.