Objective: Pericardial teratomas are rare congenital tumors which invade the developing mediastinum, compressing the venous return to the heart, leading to hydrops. Tumors, with large cystic components, have been treated previously with in utero pericardiocentesis with some success. We present the first reported case of in utero open resection of a fetal pericardial teratoma. Methods: A 31-year-old G1P0 woman was found to have a fetus with a pericardial teratoma. Hydrops developed at 24 weeks’ gestation. After counseling, open fetal resection was performed via a fetal median sternotomy. Results: Although the tumor was successfully removed, the hydrops did not resolve. In addition, over the course of 3 weeks, the mother developed maternal mirror syndrome which prompted an emergent cesarean section. Neonatal death ensued shortly after birth. Conclusions: The fetus with a pericardial teratoma complicated by hydrops is compromised. Treatment options include early delivery, aspiration of the pericardial effusion, and in utero operative resection.