Congenital intrapericardial teratoma can present in the fetal and neonatal period, but prenatal diagnosis is difficult. Its clinical course, similar to that of an anterior mediastinal mass, may be fatal if the tumor is not promptly excised. We report the case of a fetus with a large anterior mediastinal mass associated with hydramnios, pleural effusion, and ascites. Perinatal surgical removal is the only lifesaving therapy; any conservative approach in these neonates should be avoided even if critically symptomatic.