We report a case of fetal systemic hypertension. This occurred in an ex-donor twin soon after coagulation of chorionic vessels and amniodrainage performed for severe twin-twin transfusion syndrome during the 2nd trimester of pregnancy. Systemic hypertension was suspected because of a high systolic velocity through the tricuspid valve, and Bernoulli's equation was used to estimate the right intraventricular pressure. As both pulmonary arteries and ductus arteriosus were normal, the pressure in the aorta was considered to be equal to that in the right ventricle (60 mm Hg). Fetal systemic hypertension could have happened either because of a dramatic increase in placental resistances in the territory of the ex-donor twin or by reversal of the fetofetal transfusion pathological process.