Placental mesenchymal dysplasia (PMD) is a recently described entity. Because of the presence of an embryo and a multicystic placenta, it has been initially misinterpreted as a partial mole on ultrasound as well as on gross examination. However, careful microscopic examination, cytogenetic analyses, molecular studies and follow-up of children allowed to better understand this placental abnormality, allowing an antenatal diagnosis. Our purpose was to describe ultrasonographic, macroscopic and microscopic features in PMD on the basis of a literature review and our own experience. We also detailed clinical presentation, complications of pregnancy and fetopathologic associations. We discussed ethiopathogenic hypotheses as well as differential diagnoses.