Differentiation of undifferentiated connective tissue disease is generally defined as the evolution into a specific connective tissue disease, and how long it takes to differentiate is related to factors such as one’s condition and the efficacy of treatment. Of these, about 70% of patients will remain undifferentiated and about 30% will evolve into a connective tissue disease (CTD), and the incidence of evolution is higher three to five years after disease onset. As the disease progresses, the incidence of evolution decreases again, and the main CTDs that may evolve are systemic lupus erythematosus, systemic sclerosis and rheumatoid arthritis.