Anti-phosphatidylethanolamine antibodies (aPE) belong to the group of anti-phospholipid antibodies (aPL) and are directed against neutral phospholipid, connected with co-factor protein, while cardiolipin antibodies (aKL) are directed against negative phospholipid. The paper presents a study of prevalence and clinical significance of IgG aPE in 28 patients (22 women and 6 men, mean age 47.6 +/- 11.6 years) with Sneddon's syndrome (SS), which consists in cerebrovascular disturbances and extensive livedo reticularis. IgG aPE were detected by immune-enzyme assay. The upper normal limit, calculated as mean + 3SD after studying 19 healthy donors, was 0.303 optic density units. aPE were found in 15 (54%), aKL and/or lupus anticoagulant (LA)--in 6 (21%) patients with SS. aPE were found in 10 (46%) out of 22 aKL- and LA-negative patients. Among the aPE-positive patients there was a higher incidence of cortic dementia (53% vs. 8%, p = 0.02), the widening of cortical sulci, detected by means of computed tomography and magnetic resonance imaging (73% vs. 31%, p = 0.05), and mild renal syndrome (73% vs. 16%, p = 0.03). Besides, they displayed a higher rate of headaches (87% vs. 62%), chorea (33% vs. 8%), epilepsy (27% vs. 8%), non-carrying of pregnancy (91% vs. 50%), peripheral venous thrombosis (27% vs. 15%), coronary heart disease (47% vs. 31%), cardiac valvular thickening, detected by means of EchoCG (93% vs. 69%), arterial hypertension (87% vs. 54%), thrombocytopenia (20% vs. 0), anemia (40% vs. 15%); however, the difference was not significant. The results show that aPE detection, performed in addition to detection of classic immunological antiphospholipid syndrome markers (aKL and LA), increases the portion of aPE-positive patients with SS by 33%. aPE are often (in 46% of cases) found in aKL- and LA-negative patients with SS. aPE is likely to be the most significant factor of thrombosis in small arteries of the brain cortex and kidneys, which could explain their association with dementia and renal syndrome.