Objective — to carry out a clinical and morphological analysis of 6 cases of placental mesenchymal dysplasia (PMD) that is not associated with Beckwith—Wiedemann syndrome. Material and methods. Medical records, placental macroscopic and microscopic changes, histochemical (MSB staining) and immunohistochemical studies of placental tissue with antibodies against p57, CD34, smooth muscle actin, desmin, and Ki-67 were analyzed. Results. Vascular anomalies in the chorionic plate and stem villi, the increased size and edema of the stem villi during normal formation of the terminal branches of the villous tree, the lack of proliferation of villous trophoblast were the typical signs of PMD and were noted in all cases. Comparison of the results of ultrasonography with the morphological pattern of the disease suggested that there were ultrasound signs that were typical of PMD. The characteristics of the course and outcomes of pregnancy in PMD were given. The features of morphological changes in the presence of PMD concurrent with preeclampsia were found. Significant variability in p57 expression in PMD was shown and variants of changes given. There were no substantial features of the expression of desmin and smooth muscle actin in PMD. Conclusion. MDP has typical morphological and ultrasound signs. The significant variability in the levels of chorionic gonadotropin and alpha-fetoprotein and in the expression of p57 does not allow their use in the differential diagnosis of PMD. The high incidence of thrombotic events in the intervillous space and fetal vessels, as well as intrauterine growth restriction, intrauterine hypoxia, and an impaired neonatal adaptation period in PMD should be taken into account when determining the management tactics for female patients and newborns.