Undifferentiated connective tissue disease (UCTD) is a systemic autoimmune disease. This means the body’s natural immune system does not behave normally. Instead of serving to fight infections such as bacteria and viruses, the body’s own immune system attacks itself. In UCTD, autoimmunity may cause the immune system to attack specific parts of the body resulting in a variety of problems. The phrase “connective tissue disease” is used to describe the diseases of the immune system that are treated primarily by rheumatologists. These represent systemic autoimmune diseases that often involve the joints, cartilage, muscles, and skin. They can also involve any other organ system such as the eyes, heart, lungs, kidneys, gastrointestinal tract, bone marrow, nervous system, and blood vessels. Examples of connective tissue diseases include lupus, scleroderma, rheumatoid arthritis, Sjögren’s syndrome, myositis, and vasculitis. There are many people who have features of connective tissue disease; however, they do not fulfill the diagnostic criteria established for any one disease. In such circumstances, they are often considered to have “undifferentiated” connective tissue disease. Over time, people with UCTD may evolve into one of the more specific connective tissue diseases, such as lupus, Sjögren’s or scleroderma.