This term is used for a disorder of unknown cause that affects the lungs and other organ systems. It is a form of inflammation that has a granuloma as a basic structure. A granuloma is an organized swirl of cells that is seen microscopically by pathologists in biopsy material. There is sometimes associated scarring or fibrosis. The granuloma inflammation occurs in the interstitium of the lung, which is a network of cellular structures. The granuloma inflammation also occurs in the alveoli, which are rounded structures in the lung where oxygen is exchanged from the air to the blood. The granulomas also occur in lymph nodes in the center of the chest and in the airways.

Sometimes granulomas occur in other parts of the body such as other lymph nodes, liver, heart, brain and skin. Sarcoidosis may spontaneously resolve, may stabilize or may be progressive.