OBJECTIVES: Thyroid eye disease (TED) seriously affects patients' quality of life (QoL), even if the disease is stable and nonactive. Data on clinical factors negatively influencing the QoL of patients with TED and long-term outcomes are limited. This study aims to evaluate the lasting impact of TED on QoL, focusing on the effects of previous TED treatments and identifying factors influencing long-term outcomes. METHODS: A retrospective cohort study included 151 patients treated for active, moderate-to-severe and severe TED, with a mean follow-up of 8 years. RESULTS: Higher clinical activity scores at diagnosis correlated with lower QoL scores. Thyroidectomy before immunosuppressive treatment was associated with lower QoL and an increased likelihood of orbital decompression. Any disease progression necessitating second-line treatments also negatively affected QoL. A decrease in thyrotropin receptor antibodies during active treatment and early treatment initiation positively affected visual functioning. Time-dependent regression analysis demonstrated no significant trend in QoL changes over time. CONCLUSION: Our data reveal that disease severity, the timing of interventions and disease progression contribute to less favourable long-term QoL outcomes, extending years beyond active treatment. Early and accurate diagnosis and appropriate treatment can minimise poor long-term QoL in patients with TED.