Cystic fibrosis, SIHS tihk fy BROH sihs, is a hereditary disease in which certain glands in the body secrete large amounts of abnormally thick mucus. Accumulation of mucus can block the ducts of these glands and eventually may block the passageways of organs into which the ducts empty. This accumulation of mucus may damage many organs, particularly the lungs, pancreas, and liver. Cystic fibrosis, often abbreviated CF, is also called mucoviscidosis.