Placental mesenchymal dysplasia (PMD) is a rare placental pathology that sonographically mimics gestational trophoblastic diseases. However, mesenchymal dysplasia can be distinguished from other conditions by the presence of villous edema and the absence of trophoblastic proliferation in the placental tissue. This pathology has been demonstrated to be associated with fetal growth restriction, Beckwith-Wiedemann syndrome, some chromosomal abnormalities and intrauterine fetal demise. A review of the literature revealed approximately 200 articles on PMD. Nevertheless, eight articles on PMD in twin pregnancies were identified, encompassing a total of nine cases. This is the tenth case of PMD in a twin pregnancy and the fourth case of monochorionic twins in the literature. The patient was a 28-year-old primigravid woman. A portion of the placenta exhibited sonographic features consistent with PMD. Both fetuses developed hydrops fetalis at 16 weeks of gestation. The fetal karyotype demonstrated no abnormalities, and no additional major congenital anomalies were identified. Following pregnancy termination, a pathological examination confirmed PMD in the placental portion of one of the fetuses. This study aims to contribute to the existing literature on this condition, which can be challenging to diagnose and manage, particularly in twin pregnancies.