Alagille syndrome (AGS) is one of the most problematic for the diagnosis of hereditary, multisystem, cholestatic liver diseases in combination with other congenital defects. Timely diagnosis and treatment (including liver transplantation - LT) improves the quality of life (QoL), prevents irreversible liver changes, multiple organ failure and mortality. Aim – to study the possibilities and features of the differential diagnosis of AGS, the impact of complex treatment, surgical correction (including LT) on the course of the disease, the dynamics of clinical and laboratory indicators, physical development (FD) and neuropsychological development (NPD), QoL. Materials and methods. Verification of the diagnosis of AGS included clinical, biochemical, instrumental examinations, genetic markers of AGS. Quality of life was evaluated: assessment of skin itching (on a categorical scale, according to the visual analogue scale of pruritus; the level of anxiety was determined according to the Hamilton scale (modified). FD and NPD were evaluated by pediatricians and pediatric neurologists before and after treatment. The assessment of FD according to centile tables was carried out in accordance with WHO standards. The assessment of NPD was carried out: development delay for one, two, three epicrisis terms; degree of NPD delay. Results. Against the background of treatment, biochemical and clinical indicators improved. Itching of the skin (according to the categorical scale of itching, visual analogue scale of pruritus), decreased the anxiety index. The dynamics of the FD and NPD were positive. Conclusions. Modern possibilities of diagnosis of AGS include genetic and histological methods, which makes it possible to start pathogenetic therapy early, to decide the time and ways of surgical intervention (including LT). The presence of concomitant congenital defects of other organs and systems, the characteristic appearance of children with AGS require a multidisciplinary examination with the involvement of multidisciplinary specialists. Complex and timely treatment of AGS contributes to the normalization of clinical and biochemical indicators, FD, NPD, quality of life. Radical treatment of AGS by means of LT should be considered before the period of irreversible multiorgan changes, taking into account the preservation of FD and NPD. The research was carried out in accordance with the principles of the Declaration of Helsinki. Informed consent of the child and child's parents was obtained for the research. The author declares no conflict of interest.