Abstract Disclosure: M.T. Torres Torres: None. A.N. Gonzalez Bossolo: None. M.M. Mangual Garcia: None. Thyroid eye disease (TED) is an autoimmune disease of the orbital soft tissue associated with facial disfigurement, diminished quality of life, and potentially vision-threatening consequences that can occur in 40% of patients with Graves’ disease (GD). All the therapies for this condition were off-label with questionable long-term effects until 2020 when the Federal Drug Administration approved teprotumumab, a human monoclonal antibody against insulin-like growth factor-1 receptor, for the treatment of TED. Randomized placebo-controlled trials have demonstrated that teprotumumab reduces proptosis, diplopia, and Clinical Activity Score (CAS) in patients with active TED of less than 1.3 years of duration who were treatment-naïve or previously treated with < 1g of methylprednisolone equivalent therapy. Data on the efficacy of teprotumumab on cases of longer TED duration or previously treated with eye surgery or > 1g of methylprednisolone equivalent therapy for TED is limited as these patients were excluded from the trials. A 76-year-old nonsmoker male with long-standing hyperthyroidism due to GD, glaucoma, and type 1 diabetes mellitus was referred by ophthalmologist due to TED. He received radioactive iodine (RAI) for treatment of GD after failure to Methimazole therapy. After RAI, he reported progressively worsening bilateral eye edema, redness, pain, vision loss, and diplopia requiring hospitalization for an emergent orbital decompressive surgery and intravenous steroid therapy due to sight-threatening Grave’s orbitopathy. He was discharged home with oral prednisone taper down until it was discontinued 6 months later with mild improvement of symptoms. Physical exam was remarkable for bilateral strabismus, orbital chemosis, conjunctival injection and redness, eyelid swelling, limited eye motion, severely impaired visual acuity and color vision, no proptosis, and a CAS of 5 suggesting active TED. Laboratories showed biochemical euthyroidism and controlled glycemia. Teprotumumab was started 2 years and 8 months after symptom onset with marked improvement of inflammatory signs and symptoms, eye motion, visual acuity, diplopia, intraocular pressure, and CAS score decrease to 1 point suggesting inactive disease within 4 weeks of therapy without adverse side effects. This case describes the positive effects of teprotumumab in a patient with characteristics not previously studied such as active TED of longer duration than in clinical trials, previous treatment with orbital surgery or > 1g of methylprednisolone equivalent therapy, and increased IOP. Rather than drawing conclusions, our goal is to create awareness and promote further research of teprotumumab and novel agents in patients with TED with previously uncharacterized presentations as it may have important implications for their management including significant improvement in their quality of life. Presentation: Friday, June 16, 2023