A primary pleural effusion at birth is an uncommon finding, with only 10 cases recorded in the literature. Recently, 2 additional ones have been observed and are reported herein to inform others of the existence of such an entity and of the possibility of its early diagnosis. Case Reports Case I: A white female infant was born at Crouse-Irving Hospital, Syracuse, N. Y., to a gravida V mother. Dyspnea was evident immediately. A pink color and fair pulse could be maintained only with the administration of oxygen by intermittent positive pressure following intubation. A portable chest x-ray film disclosed apparent total lack of aeration of both lungs (Fig. 1). Hydrothorax was suggested by the anesthesiologist, and a thoracentesis ninety minutes after birth yielded 20 c.c. of clear yellow fluid from each side. Improvement in the infant's color and respiration followed, but soon the infant again appeared distressed. A repeat portable chest radiograph (Fig. 2) showed a right pneumothorax, and underwater drainage with chest tube was then established. Following removal of an additional 45 c.c. of fluid from the left side, a tension pneumothorax occurred, necessitating a second chest tube (Fig. 3). The infant's condition stabilized, and supportive measures were instituted. She seemed to do well, but at fifteen hours of age respirations and pulse suddenly ceased. Autopsy revealed bilateral pneumothorax, bilateral pleural effusions, hepatomegaly, and an accessory spleen. In an attempt to demonstrate the integrity of the thoracic duct so as to explain the source of the effusion, methylene blue was injected into its origin in the lumbar region. The dye passed throixgh the mediastinal area without leakage into either pleural space. Case II: A 12-lb., 1-oz. male child was transferred to Syracuse Memorial Hospital three hours after birth at another institution. The infant was the product of a full-term pregnancy during which the mother had an excessive weight gain but no elevated blood pressure or glycosuria. The delivery was difficult and required the use of midforceps. Marked polyhydramnios was noted. The baby breathed and cried spontaneously, but was noted to be in respiratory distress immediately He was cyanotic when not receiving oxygen. Examination revealed dullness and absent breath sounds over the left side of the chest. Substernal retractions were marked. Heart sounds were normal, best heard in the right side. The abdomen was soft, but diffusely distended without evidence of organomegaly or masses. Large bilateral hydroceles were easily reduced. A chest radiograph revealed opacification of the left thorax (Fig. 4). Since a questionably distended loop of bowel was noted in the midabdomen, a barium-enema examination was performed to exclude the possibility of herniation of bowel into the chest. A thoracentesis on the left yielded 160 c.c. of clear yellow fluid. Immediate improvement was noted in the patient's color and aeration of the left side.