Isolated pleural effusion, so called primary pleural effusion denotes a pleural effusion without documented etiology such as a cardiac, inflammatory, iatrogenic problem or fetal hydrops. Chromosomal anomaly such as Down syndrome may be associated with isolated pleural effusion. The content of the isolated pleural effusion is mostly chylous, and isolated non-chylous pleural effusion in neonate is rare. We experienced 2 cases of isolated non-chylous pleural effusion. They had neither cardiac problem nor other sign of hydrops fetalis. Imaging diagnosis was done by plain chest radiography and subsequent ultrasonogram. One of them was diagnosed to Down syndrome by karyotyping. They were fared well after diagnostic and therapeutic thoracentesis. We describe 2 cases of non-chylous pleural effusion and review a few English-language case reports of this entity.