Lymphangitic carcinomatosis of the lung is a late and fatal manifestation of cancer. The diagnosis is seldom made ante mortem. Four patients with breast cancer had autopsy-proven lymphangitic metastases of the lung. Of these patients, two had normal chest x-rays and three had normal ventilation lung scans. The perfusion lung scans of all four showed irregular peripheral perfusion defects. Autopsies showed permeation of the lymphatics by tumor and tumor emboli in small arteries and arterioles.