49 of 82 acute pediatric leukemia cases have chest X-rays showing 71.4% abnormalities, pulmonary changes 27, mediastino-hilar glandular enlargement 19, pleural effusion 3, cardiac enlargement 10, rib destruction 2. Bronchopneumonic appearance is the most common pulmonary manifestation, but nodular lesion is more characteristic. Five autopsies are reviewed and the relation of the X-ray findings to the possible pathologic basis is discussed. The X-ray findings are varied and seem to have no rules. If bronchopneumonic or pneumonic consolidation is manifested and concomitant respiratory symptoms and signs are present, infection should be considered the cause. The following conditions may herald leukemia: pulmonary changes not responsive to treatment for infection, but responsive to antileukemic treatment with signs of mild respiratory tract involvement, pulmonary changes associated with mediastino-hilar glandular enlargement, pulmonary nodular lesion associated with glandular enlargement, moderate effusion accumulating quickly after paracentesis and responsive to acute leukemic therapy, cardiac and bony changes.