OBJECTIVES The aim of this report is to present the diagnostic path and treatment of oral manifestations related to IgG4 disease. This disease has an autoimmune nature and it has been identified as a diagnostic entity only recently. IgG4 disease can affect different organs, mostly pancreas, biliary tree, salivary glands, peri-orbital tissues, kidneys, lungs, lymph nodes, meninges, aorta, breasts, prostate, thyroid, pericardium and skin. The oral manifestations are heterogeneous and the disease can be difficult to diagnose, as they may overlap with symptom-atological and clinical conditions of other oral conditions, such as inflammation caused by bullous diseases (e.g. pemphigus and pem-phigoid), autoimmune disease (e.g. oral lichen planus), related plaque gingivitis and oral cancer. Currently in the literature only a few epidemiological data of diagnostic procedure are reported. Biopsy represents the gold standard for diagnosis, as it highlights the histopathological peculiarities that characterize this condition. MATERIALS AND METHODS This case report describes a 73-years old female patient, presenting to the Dental Emergency Department of the San Paolo hospital in Milan, with pain to the right gum and to the right buccal mucosa for two weeks. The patient felt no benefit following treatment with chlorhexidine digluconate-based mouthwash. She had a diagnosis of IgG4 disease confirmed by the biopsy of lacrimal glands. After intraoral physical examination the presence of slight plaque and calcoulus accumulations was shown, as well as a picture of erosion of the gingival epithelium at the level of all the quadrants, which was compatible with desquamative gingivitis. It was also shown an ulcerated lesion at the level of the right buccal mucosa. Actually, clinical data were not sufficient to make a diagnosis. For this reason the patient underwent multiple incisional biopsy in order to obtain a histopathological diagnosis. RESULTS The histological findings showed a diffusely ulcerated oral mucosa and a dense lymphoplasmacytic inflammatory cell infiltrate in the sample, obscuring its architecture. Lymphoid follicles with germinal centres were present. All the plasmacells expressed IgG in their cytoplasm and the IgG4 fraction was greater than 0.4 or anyway greater than 50 per high-power field. The histological findings, supported by a remote pathological history positive for IgG4 disease and physical examination, was compatible with salivary changes related to IgG4 disease. CONCLUSIONS After obtaining histological diagnosis the patient was treated with topical steroids, namely clo-betasol gel 0.05% for a total of 10 weeks with decreasing applications. It was not necessary to send the patient to other specialist because of the absence of systematic symptoms related to IgG4 disease. After 3 months from the prescription of therapy with clo-betasol gel, a control was per-formed and a complete resolu-tion of the signs and symptoms of the disease at the level of oral cavity was observed. Subse-quently the patient was scheduled for a six-months follow-up in order to monitor the progression of oral manifestation of IgG4 disease. CLINICAL SIGNIFICANCE IgG4 disease is a rare condition that in a few cases involves the cervical-facial district. It has only recently been recognized as a well defined disease characterized by pathognomonic histological and immunohistochemical findings that allow a correct diagnosis and an adequate therapeutic treatment. In oral manifestation of IgG4 disease there are no pathognomonic clinical signs and this can lead to a diagnostic delay causing an accentuation of the symptoms and grater discomfort for the patient.