The paper presents two cases of a rare condition, such as a concurrence of a complete hydatidiform mole and a developing fetus with a normal placenta in multiple pregnancy. It describes the features of the course of pregnancy in this condition, the ultrasound pattern of the latter and its morphological and immunohistochemical signs. The concurrence of a complete hydatidiform mole with intact placental tissue and a viable fetus poses a pressing problem of whether it is possible and expedient to prolong pregnancy associated with the high risk of life-threatening complications, including persistent trophoblastic disease. The paper discusses the principles of diagnosis of this pathology, differential diagnosis, and patient management tactics.