Thyroid eye disease (TED) is an autoimmune process characterized by extraocular muscle and orbital fat remodeling/expansion resulting in swelling, pain, redness, proptosis, and diplopia. Teprotumumab, an insulin-like growth factor-I receptor inhibitor, demonstrated improvements in TED signs and symptoms in three adequately powered clinical trials of 24 weeks duration. Here we analyze the long-term maintenance of responses with teprotumumab from these trials. A total of 112 patients who received 7 or 8 infusions of teprotumumab in the Phase 2, Phase 3 (OPTIC study), and OPTIC Extension (OPTIC-X) studies were included in this analysis. Responses, including clinical activity score (CAS ≥2-point improvement), the European Group of Graves' Orbitopathy ophthalmic composite outcome, diplopia (≥1 Gorman grade improvement), proptosis (≥2 mm improvement), Overall (improvement in proptosis + CAS), and disease inactivation (CAS ≤1), were assessed and pooled from study baseline to week 24 (formal study) and up to week 72 (formal follow-up). Graves' Ophthalmopathy quality-of-life (GO-QoL) scores were also assessed. Outcomes included the percentages of observed patient responses from the study baseline. Additional alternative treatments for TED were assessed as a surrogate of persistent benefit from week 24 through week 120 (extended follow-up). Studies differed in the timing of follow-up visits, and data from some visits were unavailable. At week 72, 52/57 (91.2%), 51/57 (89.5%), 35/48 (72.9%), 38/56 (67.9%), and 37/56 (66.1%) of patients were responders for CAS, composite outcome, diplopia, proptosis, and Overall response, respectively. The mean reduction in proptosis was 2.68 mm (SD 1.92, = 56), mean GO-QoL improvement was 15.22 (SE 2.82, = 56), and disease inactivation (CAS ≤1) was detected in 40/57 (70.2%). Over 99 weeks following teprotumumab therapy, 19/106 (17.9%) patients reported additional TED therapy during formal and extended follow-up. The long-term response to teprotumumab as observed 51 weeks after therapy was similar to week 24 results in the controlled clinical trials. Inflammatory and ophthalmic composite outcome improvements were seen in 90% of patients with nearly 70% reporting improvement in diplopia and proptosis. Further, 82% of patients in this analysis did not report additional TED treatment (including surgery) over 99 weeks following the final teprotumumab dose.