Thyroid-associated ophthalmopathy is the most common cause of proptosis in adult female, especially those with positive thyroid antibody. Sometimes, other diagnoses should be considered. A 45-year-old female presented with progressive right proptosis and mild diplopia for 2 years. One year earlier, she had been diagnosed with thyroid-associated ophthalmopathy because of abnormal thyroid autoantibody. Computed tomography scan showed a 2.4- × 1.9- × 1.6-mm heterogeneous soft-tissue density lying above the left eye. Excisional biopsy of this mass revealed the histopathologic diagnosis of pleomorphic adenoma. This case highlights the need for including other diagnoses such as pleomorphic adenoma in the differential diagnosis of patients with proptosis, diplopia and abnormal thyroid antibody.