Background. Nitric oxide (NO) is a short-lived molecule, involved in neurotransmission, anti-inflammatory action, diminished platelet aggregation, increased angiogenesis and regulation of vascular tone. Reduced availability of NO leads to dysfunction of endothelium and contributes to disease manifestation such as hypertension and peripheral artery disease. Antiphospholipid syndrome (APS) is a systemic autoimmune disease characterized by thrombotic events and/or pregnancy morbidity with the persistent presence of antiphospholipid antibodies. Recent studies suggest that thrombosis may be linked to diminished production of NO in endothelial cells. The aim of the present study was to determine whether patients with APS display diminished NO-stimulated vasodilation or not. Since vasodilation capability decreases with aging, we determined endothelium-dependent and endothelium-independent vasodilator response of cutaneous microvasculature of APS patients and healthy controls in different age groups. Methods. 34 patients with APS and 34 healthy age and sex-matched controls completed the study. Participants were asked to avoid coffee, tea or energy drinks on the day of the measurements. We measured laser Doppler flux of microvessels in non-glabrous skin. Iontophoresis of acetylcholine, which stimulates NO production in endothelial cells, was used to assess endothelium-dependent vasodilation and iontophoresis of sodium nitroprusside, a direct NO donor, was used to assess endothelium-independent vasodilation. Data were analysed using ANOVA followed by Dunnett’s test. The study was approved by the National Medical Ethics Committee; written informed consent was obtained from each subject. Results. Endothelium-dependent vasodilation in three out of four group did not differ (82.1 ± 15.3 PU in patients aged 22 to 38 vs. 81.6 ± 13.0 PU in age matched controls; 94.2 ± 15.3 PU in patients aged 39 to 49 vs. 71.7 ± 11.7 PU in age matched controls). In the age group of 50-74 years it was significantly smaller in patients compared to healthy controls (54.7 ± 10.5 PU in patients vs. 88.2 ± 10.3 PU in age matched controls) (t-test, p<0,050). Endothelium-independent vasodilation in all age groups of patients did not differ from the control group (35.3 ± 8.2 PU in patients aged 22 to 38 years vs. 66.2 ± 22.2 PU in age matched controls; 33.1 ± 10.5 PU in patients aged 39 to 49 years vs. 49.0 ± 11.7 PU in age matched controls, 27.3 ± 3.7 PU in patients aged 50 to 74 years vs. 33.5 ± 8.1 PU in age matched controls). Conclusion. Vasodilation capability of patients with APS is altered. For more precise determination of these alterations further research is required, which should take into account the impact of certain drugs that are widely used for the treatment of APS patients on vasodilation.