Background: Ocular adnexal IgG4-related sclerosing disease (IgG4-SD) has been categorized as a novel disease entity. It is characterized by stromal sclerosis and an infiltration of mass-forming lymphoplasmic cells containing many IgG4-positive plasma cells. Although ocular adnexal tissue involvement has been increasingly reported, a focal nodular sub-brow mass is not typical in an IgG4-SD presentation. We report a rare case of probable ocular adnexal IgG4-SD that clinically mimicked eyelid pilomatrixoma., Case Presentation: A 42-year-old woman presented with a nodular mass in her left sub-brow area. The initial clinical impression of her lesion was eyelid pilomatrixoma. However, the final pathologic diagnosis was IgG4-SD, but extranodal marginal zone B-cell lymphoma could not be excluded. The patient underwent testing to determine tumor malignancy and systemic IgG4-SD involvement. Laboratory testing showed normal IgG and IgG4 serum levels and imaging revealed no remarkable findings. Oral prednisolone was administered and slowly tapered to manage the possible remnant lesion and to prevent disease recurrence. Two years after initiating therapy, there was no evidence of relapse. The patient is under close surveillance for signs of recurrence, systemic involvement, and potential malignant transformation., Conclusions: We found an unusual case of probable ocular adnexal IgG4-SD, which presented as a unilateral restricted mass involving the sub-brow area. Although the mass was surgically removed, systemic steroid treatment and long-term surveillance were initiated due to the possibility of recurrence, the potential association with systemic disease, and the potential development of extranodal mucosa-associated lymphoid tissue (MALT) lymphoma.