Undefined (undifferentiated) connective tissue disorders, or undifferentiated connective tissue disease, describes a condition with symptoms and test results that are similar to systemic autoimmune disorders or connective tissue disease. But the reason they are “undifferentiated” is that they don't have enough characteristics to be classified as a well-defined connective tissue disease, such as rheumatoid arthritis, lupus, or scleroderma.

Symptoms are similar to connective tissue diseases, such as fatigue, fever, and just feeling unwell. They may also include dry eyes and mouth, hair loss, joint inflammation and pain, ulcers in the mouth, a positive ANA test, Raynaud's phenomenon, and photosensitivity.

Treatment includes the use of non-steroidal anti-inflammatory drugs and avoiding exposure to extreme temperatures.

It is currently thought that fewer than 20% of patients with this condition go on to develop a definite connective tissue disease. And as many as one-third will experience a remission of their symptoms.