OBJECTIVE: To summarize the clinical characteristics of patients misdiagnosed with IgG4-related disease, to analyze the reasons of misdiagnosis and to improve the clinical recognition of the disease. METHODS: The general data, clinical manifestations, laboratory examination results and pathological features of 17 patients with IgG4-related diseases misdiagnosed outside the hospital were retrospectively analyzed. RESULTS: Among the 17 patients, there were 9 males and 8 females with a median age of 45 years, and the median time from onset to diagnosis was 12 months. Most patients' initial admission department was not rheumatology or immunology department. Six of the 17 patients were eventually diagnosed with lymphoproliferative disease, 4 with autoimmune disease, and 2 with infectious disease, Rosai Doffman disease, desmofibromatosis, highly differentiated mucoepidermoid carcinoma of the bottom of the mouth, hypereosinophilic syndrome, asthma and allergic rhinitis in 1 case each. The typical sites of IgG4-related disease were involved in 14 patients, including 6 cases of parotid gland, 2 cases of submandibular gland, 3 cases of pancreas and 2 cases of retroperitoneal lesions. Serum IgG4 was elevated in 10 patients, serum IgG4/IgG value was higher than 10% in 7 patients, serum IgE was increased in 7 patients, complement was decreased in 4 patients, and eosinophilic granulocytes were increased in 3 patients. Pathological biopsy was performed in 15 patients, and infiltration of lymphocyte was observed in 10 patients, IgG4+ plasma cells were present in 5 patients, the ratio of IgG4+ plasma cells to IgG+ plasma cells was less than 40% in 4 patients and greater than 40% in 1 patient. However, none of the 15 patients had the storiform pattern of fibrosis and obliterative phlebitis. CONCLUSION: A variety of diseases can perform as IgG4-related disease witih typical sites involved, elevated serum IgG4, even can be characterized by pathological IgG4+ plasma cells infiltration. Physicians should pay attention to the differential diagnosis and comprehensively evaluate the patient's clinical manifestations, and laboratory results. Timely and even repeated pathological biopsy is also needed for definite diagnosis.