Placental mesenchymal dysplasia is an uncommon disorder in which the placenta is enlarged with abnormal, large, and often cystic villi with dilated and/or thick-walled vessels. These placental changes can mimic a partial hydatidiform mole but in contrast to a partial mole can coexist with a fully viable fetus. Fetal anatomical and vascular anomalies frequently coexist with placental mesenchymal dysplasia. In this case, placental mesenchymal dysplasia was associated with preterm labor at 33 weeks' gestation, fetal compromise, and a large abdominal mass with a large hepatic cyst that was de-roofed at exploratory laparotomy. The neonate remained critically ill with hypoxic ischaemic encephalopathy and coagulopathy and died despite intensive care. Biopsy and autopsy findings showed a large cystic mesenchymal hamartoma affecting the left lobe of the liver. This appears to be the 3rd histologically confirmed association of placental mesenchymal dysplasia with mesenchymal hamartoma of the liver in the English language literature.