To determine the extent of superior oblique enlargement in thyroid eye disease (TED) by comparing the cross-sectional superior oblique areas of TED patients with those of unaffected control subjects. The medical records of TED patients treated for strabismus from January 2005 to January 2016 were reviewed retrospectively for demographic and surgical data. The cross-sectional superior oblique area was compared to age-matched controls on high-resolution orbital computed tomography (CT) using a standardized protocol. A total of 46 TED patients and 18 controls were included. The mean superior oblique cross-sectional area in TED subjects was 250% larger than in controls (22.88 ± 6.64 mm2 vs 9.32 ± 1.85 mm2. The mean cross-sectional area was >3 standard deviations from the mean of the control group in 96% of TED patients. Superior oblique enlargement in TED may occur more frequently than generally recognized, challenging the notion that TED is primarily a disease of the rectus muscles.