Evolution of immunopathological diseases is usually slow and progressive. Non-differentiated collagen disease (NDC) or the term "undifferentiated connective tissue disease" (UCTD) represents a stage of disease where clinical symptoms and serological abnormalities suggest autoimmune disease, but they are not sufficient to fulfill the diagnostic criteria of any well-established connective tissue disease (CTD) such as systemic lupus erythematosus (SLE), Sjögren's syndrome, mixed connective tissue disease (MCTD), systemic sclerosis (SSc), polymyositis/ dermatomyositis (PM/DM) or rheumatoid arthritis (RA). 30-40 percent of patients presenting undifferentiated profile develops and reaches the stage of a well defined systemic autoimmune disease during five years follow up, while 60 percent remains in an undifferentiated stage.In the stage of NDC, immunoregulatory abnormalities and endothelial dysfunction are present. In conclusion, NDC represents a dynamic state, and it is important to recognize the possibility of a progression to a definite systemic autoimmune disease.