The objective: to evaluate the clinical effectiveness of L-arginine in the prevention of preeclampsia and reduction of other perinatal risks in patients with preclinical gestational endotheliopathy (GE).Materials and methods. A comparative clinical study was performed at the clinical base of the Department of Obstetrics and Gynecology N. 1 of the Vinnytsya National Pirogov Memorial Medical University. 116 pregnant women with preclinical GE (main group), which was diagnosed by laboratory and instrumental research (microalbuminuria and endothelium-dependent vasodilatation), took part in the study. The patients of the main group were divided into clinical subgroups: 31 pregnant women with GE in subgroup A received acetylsalicylic acid (ASA) at a dose of 75 mg per or per day; 33 patients with preclinical GE from subgroup B received L-arginine at a dose of 4-4.2 g per or per day; 52 pregnant women with preclinical GE who refused prophylactic treatment were included in the subgroup C. The control group involved 58 pregnant women with a physiological gestation and without GE.The clinical effectiveness of the therapy was assessed by comparing the number of cases of perinatal pathology in the I, II and III trimesters.Results. The use of L-arginine as an alternative preventive therapy for the development of preeclampsia and other perinatal pathology made possible to reduce the rate of preeclampsia significantly (RR 0.19, 95% CI: 0.05-0.77; p=0.02) and placental hyperplasia/hypoplasia (RR 0.17, 95% CI: 0.04-0.68; p=0.01), compared to patients who did not receive any preventive treatment. In pregnant women with early-onset gestational endotheliopathy who received L-arginine, placental dysfunction was not diagnosed in the II and III trimesters of pregnancy and there were no cases of fetal growth retardation. The use of L-arginine was not associated with side effects and/or adverse reactions in the proposed dose and frequency of administration and can be considered beneficial for the mother and the fetus.Conclusions. Prescribing ASA and L-arginine drugs for pregnant women with a moderate degree of perinatal risk (preclinical GE) made possible not only to prolong pregnancy, but also to prevent the development of severe perinatal pathology. A more pronounced clinical effectiveness of the course prescription of solution of L-arginine per or (daily dose of L-arginine - 4.0-4.2 g) in pregnant women with preclinical form of GE may be associated with the endotheliotropic protective effect of the drug.The appropriateness of using L-arginine during pregnancy is still debated, and further researches are needed to determine the optimal dosage, initial period for using and duration for the best prophylactic or therapeutic effect.