Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 56 7 2018 08 13 478 481 EN Leila Pourali Department of Obstetrics and Gynecology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Sedigheh Ayati Department of Obstetrics and Gynecology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Parvaneh Layegh Department of Radiology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Atieh Vatanchi Department of Obstetrics and Gynecology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Zahra Rastin Department of Obstetrics and Gynecology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Azadeh Shourvi Department of Obstetrics and Gynecology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. 2017 07 09 2017 12 18 Persistent low level of beta-hCG (PLL) is defined as rising hCG level no more than two-fold over a three months period. Almost many types of PLL can lead to the wrong diagnosis. Here, we presented two cases of the retained product of conception (RPOC) with persistent low levels of beta-hCG. Both cases were presented with persistent low levels of beta-hCG and abnormal uterine bleeding since first-trimester pregnancy termination. Ultrasonography revealed a vascular mass with extension from the endometrial cavity to myometrium imitating gestational trophoblastic disease (GTD) or arteriovenous malformation (AVM). The final pathologies of both cases were retained product of conception. Imaging features of RPOC can closely imitate those of an AVM or GTN; so, hysteroscopy is one of the best non-invasive procedures which may be helpful in diagnosis and selection of appropriate treatment especially in young patients who desire to preserve their fertility.   https://acta.tums.ac.ir/index.php/acta/article/view/6589 https://acta.tums.ac.ir/index.php/acta/article/download/6589/5133