BACKGROUND Immunoglobulin G4 (IgG4)-related disease is immune-mediated and was first proposed as a defined entity after studies on patients with autoimmune pancreatitis. Since then, it has been reported in many organs. Involvement of the ovaries is rare, and to our knowledge, only 2 cases have been reported in the literature. IgG4-related disease is associated with increased serum IgG4 levels. Organ involvement includes a lymphoplasmacytic infiltrate, fibrosis, and obliterative phlebitis, with immunohistochemistry showing IgG4-positive plasma cells. This report is of a case of IgG4-related disease involving the right ovary. CASE REPORT A 47-year-old woman presented with a right ovarian cyst. An ultrasound scan revealed a complex right ovarian cyst with multiple septations. The hormonal profile and tumor markers were unremarkable. Gross examination showed fragments of cyst wall. Histologic examination revealed a follicular cyst, surrounded by a dense lymphoplasmacytic infiltrate rich in eosinophils, partially obliterative phlebitis, and fibrosis. Immunohistochemically, IgG marked most of the plasma cells, of which 70% expressed IgG4, with a count >50 cells per high-power field. Subsequent testing of serum IgG4 showed that the level was elevated (330 mg/dL). A diagnosis of IgG4-related disease was made. CONCLUSIONS Ovarian involvement by IgG4-related disease is rarely described in the literature. Our patient is likely to be the third case. We believe that cumulative findings from our case along with the 2 already reported cases increase awareness and may establish a framework for building more objective criteria to define this entity in the ovaries, similar to what has been achieved in some other organs.