Selective intrauterine growth restriction (sIUGR) is a major complication of monochorionic pregnancies, with potentially high risk of intrauterine fetal death or neurological dysfunction in both fetuses. Diagnostic ultrasound has contributed to the understanding of the pathophysiology of sIUGR and allowed to propose a classification. That, in turn, allows to interpret a wide clinical variety of sIUGR and, depending on the type, to propose a specific clinical management. The introduction of diagnosis based on Doppler studies enables the correct diagnosis of the disorders, fetal monitoring, to determine the prognosis and optimal strategies, and to propose the best therapeutic intervention.