The article contains a literature overview about twin reversed arterial perfusion (TRAP) syndrome. It is a specific complication, that affects 2,6 % of monochorionic multiple pregnancies. Left untreated twin reversed arterial perfusion syndrome leads to 50 % perinatal mortality of a normal twin. Nowadays there are a lot of etiological, pathophysiological and diagnostic questions. Hemodynamic theory, being the leader in pathogenesis of TRAP, holds that vascular anastomoses cause its development in the third week of gestation. The condition is associated with large arterio-arterial anastomose which creates the pressure gradient and conduce the reversed flow in the umbilical аrtery. In the reversely perfused twin there is no cardiac development at all or just rudimental heart can be detected. The second twin perfuses the acardiac twin during the whole pregnancy. First trimester scan is the diagnostic standard of TRAP. It is necessary to differentiate this pathology with other monochorionic multiple complications and tumor-like formations. Timely TRAP diagnosis and optimal treatment and management can increase the survival rate of pump twin and decrease perinatal mortality.