We report a unique case of a rare prenatal diagnosis of transient myeloproliferative disorder mimicking congenital leukemia, since child had no features associated with Down syndrome. Leukemic process is usually detected at birth or very shortly thereafter. Diagnosis of congenital leukemia was suspected in third trimester of pregnancy. During ultrasound examination we found hydrops foetus, pericardial effusion, hypoechoic hepatosplenomegaly with “starry night” appearence and polyhydramnios. After delivery by Caesarean section in 36th week of pregnancy, peripheral blood examination revealed leukocytosis and thrombocytopenia. Bone marrow aspiration showed 20% of myeloid blasts typical for megakaryoblastic leukemia/transient myeloproliferative disorders. Trisomy 21 was present only in blasts and GATA1 mutation was also confirmed. Based on an early prenatal suspicion and quick and intensive postnatal intervention patient survived.