Diffuse parenchymal lung disease (DPLD), also known as interstitial lung disease, refers to a group of lung diseases, affecting the alveolar epithelium, pulmonary capillary endothelium, basement membrane, perivascular and perilymphatic tissues. The term DPLD is used to distinguish these diseases from obstructive airways diseases. Most types of DPLD involve fibrosis, but this is not essential; indeed fibrosis is often a later feature. Hence the term pulmonary fibrosis has fallen out of favor.