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To propose and validate a measure of medial wall bowing in thyroid eye disease (TED) and to assess the clinical correlates of bowing in TED.In this cross-sectional cohort study, all patients affected with TED seen by a single specialist over a 2-year period were screened for study entry. Eligible participants were adults with clinical evidence of TED and either CT or MRI of the orbits. Exclusion criteria included prior history of decompression surgery and/or medical or other ophthalmic conditions that could alter the orbital anatomy. The primary outcome measure was prevalence of medial wall bowing. Secondary outcomes included the associations between medial wall bowing and exophthalmometry, diplopia, rectus muscle restriction, dysthyroid optic neuropathy (DON), strabismus, and quality of life. Medial wall bowing was defined as medial divergence of the medial wall from a straight line drawn between the anterior lacrimal crest and the middle of the optic canal and measured radiographically using axial images of the orbits. Volumetric analysis of bowing was performed on a sample of orbits with and without bowing. Volumetric and axial single slice measurements were compared. Bivariate statistics were performed.The final sample included 112 orbital images from 56 patients with TED. Medial wall bowing was found to be evident in 11.6% (n = 13/112) of orbits. Medial wall bowing was significantly associated with greater Hertel measurements, horizontal and vertical muscle restriction, ocular surface symptoms and Clinical Activity Score, as well as lower quality of life scores. Patients with demonstrable medial wall bowing were more likely to be affected by optic neuropathy, diplopia (Gorman score ≥ 1), strabismus, or horizontal muscle restriction. Analysis of the volume for medial wall bowing demonstrated that the height of the arc at the peak of bowing on an axial image of a 2-dimensional CT scan correlated highly with the total volume of bowing (r = 0.90, p < 0.001).The identification of medial wall bowing on CT or MRI is associated with clinical measures of disease severity, including diplopia and DON.