Agenesis of the lung is an extremely rare anomaly t has been reported as an isolated defect or in associationwith other congenital malformations. The case of a full term newborn girl with isolated right lung agenesis is describ-ed. She was asymptomatic, except for slight tachypnea in the first few days of life, which was associated to meco-nium in the amniotic fluid but not in her tracheal aspirates, Clinically there was evidence of displacement of heart'sapical impulse and sounds to the right side of the thorax, which on chest X ray films looked opaque, with intercostalspace retraction and mediastinal displacement to the same side. Absence of right pulmonary artery, veins and pa-renchima were documented by X ray and radionuclide angiography and pulmonary scintigraphy. Heart and abdo-minal ultrasonography showed no additional abnormalities. She was dismissed from hospital stage 12 days and hercourse was uneventfuil until age seven weeks, when she was admitted because of acute pneumonia which causedher death a few days later.(Key words: Lung agenesis, pulmonary artery, newborn.]