To evaluate clinical features of patients who first present with orbital symptoms and signs due to undiagnosed sinonasal pathology. Retrospective chart review for patients seen at Moorfields Eye Hospital between 1969 and 2020. Patient demographics and clinical features were reviewed. Four hundred and forty-eight patients (250 males; 56%) presented to ophthalmologists with undiagnosed sinonasal pathologies, the patients attending at an average age of 47 years and having first symptoms at an average age of 46 years. The commonest presenting symptoms were proptosis (153 patients; 34%), orbital ache or pain (133; 31%), periorbital swelling (130; 29%), and diplopia (98; 22%). Eighty-seven patients (20%) had a corrected acuity of 6/18 or worse, and 66 (16%) had an ipsilateral relative afferent pupillary defect. There was 2.3 mm relative exophthalmos (median 2 mm; range 0-17 mm) in patients with unilateral disease, an orbital mass was palpable in 218 patients (49%), ocular movements were reduced in 252/448 (56%), and nonaxial displacement of the globe was recorded in 296/424 (74%). The commonest pathologies were sinus mucoceles (38%), sinus carcinoma (11%), and granulomatous polyangiitis (10%). Multivariate regression analysis of mass lesions identified periorbital pain (odds ratio, 6.0; 95% confidence interval, 1.7-21.5; P = 0.005) and reduced motility (odds ratio, 3.2; 95% confidence interval, 1.1-9.0; P = 0.03) as features most predictive for undiagnosed sinonasal malignancy. This study describes a large group of patients in whom unknown midfacial masses presented initially to the ophthalmologist: Mucoceles and sinonasal malignancy were the commonest lesions, and nonaxial globe displacement-particularly inferolateral, lateral, or upward-is commonly associated with sinonasal pathology. Pain and reduced ocular movements significantly favor a malignant, rather than benign, tumor.