Undifferentiated connective tissue disorders are sometimes easily misdiagnosed because the cause of undifferentiated connective tissue disorders is unclear, and the symptoms that manifest are generally related due to genetic factors, abnormalities in the immune system, viral infections, and other factors. Undifferentiated connective tissue disease is a group of diseases that have the clinical and serologic manifestations of certain connective tissue diseases, but do not meet the diagnostic criteria for any particular connective tissue disease. The clinical manifestations of the disease are varied and may belong to the early stages of diffuse connective tissue disease or the tonoplastic form, or it may be a stand-alone disease. Undifferentiated connective tissue disease may initially present with non-specific symptoms such as malaise, low-grade fever, and enlarged lymph nodes, while the most frequent symptoms of specific manifestations are arthralgias, Raynaud’s phenomenon, and cutaneous and mucosal manifestations, and involvement of vital organs such as the kidneys and the central nervous system is rare. Therefore, undifferentiated connective tissue disease is easy to be misdiagnosed clinically, and it is recommended that patients with the above manifestations or those who have already been diagnosed with connective tissue disease should consult the Department of Rheumatology and Immunology in a timely manner.