Objective: To review what is currently known about placental mesenchymal dysplasia (PMD) including imaging techniques for diagnosis and differentiation from a molar pregnancy, genetics, maternal/fetal effects, and management. Evidence Acquisition: A literature search by research librarians at 2 universities was undertaken using the search engines PubMed and Web of Science. The search terms used were "etiology" OR "cause" OR "risk" OR "risks" OR "epidemiology" OR "diagnosis" OR "therapy" OR "prognosis" OR "management" AND "placental mesenchymal dysplasia" OR "placenta" AND "mesenchymal dysplasia." No limit was put on the number of years searched. Results: The etiology of PMD remains uncertain, although there are a number of theories on causation. An elevated maternal serum α-fetoprotein level, slightly elevated human chorionic gonadotropin level, normal karyotype, multicystic lesions on ultrasound, and varying degrees of flow within cysts using color Doppler (stained-glass appearance) are helpful in making the diagnosis. On pathologic examination of the placenta, PMD is differentiated from molar pregnancy by the absence of trophoblastic hyperplasia. Fetal complications of PMD include hematologic disorders, Beckwith-Wiedemann syndrome, liver tumors, fetal growth restriction, preterm delivery, and intrauterine fetal demise. Maternal complications include gestational hypertension, preeclampsia, HELLP (hemolysis, elevated liver function tests, low platelets) syndrome, and eclampsia. Conclusions: Accurate diagnosis of PMD is imperative for appropriate management and surveillance to minimize adverse maternal and fetal outcomes. Relevance: The importance of a correct diagnosis of PMD is important because it can be misdiagnosed as a partial molar pregnancy or a complete mole with coexisting normal fetus, and this can result in inappropriate management.