Background: Orbital complications arising from acute rhinosinusitis (ARS) are a major concern for clinicians and serve as important warning indicators of ARS. Prompt recognition and appropriate management are crucial for preventing potential vision-threatening sequelae. Orbital complications of rhinosinusitis are markedly more common in children than in adults. The aim of this study was to investigate the clinical characteristics and treatment outcomes of orbital complications of ARS in adult patients. Methods: This retrospective observational cohort study analyzed the medical records of 176 patients admitted for orbital cellulitis/abscess (ICD code: H050) who underwent orbit or paranasal computed tomography from January 2001 to February 2022 at a tertiary hospital. Results: Eighteen adults with a mean age of 53.2±18.9 years were diagnosed with orbital complications due to ARS: five (27.8%) had preseptal cellulitis, eight (44.4%) had orbital cellulitis, and five (27.8%) had subperiosteal orbital abscess. None of the patients had an orbital abscess or cavernous sinus thrombosis. All patients had unilateral orbital complications (7 right and 11 left) and were managed with intravenous antibiotics for an average of 10.3±6.6 days. Five patients with subperiosteal orbital abscesses underwent intranasal endoscopic drainage at an average of 1.4±1.9 days after admission, while two patients required additional external drainage. Complete recovery was observed in all patients. Conclusions Conservative antimicrobial therapy can be effective for treating orbital complications from ARS, and not all adult patients require immediate surgical intervention for subperiosteal abscesses. Nonetheless, careful monitoring is essential, and an ophthalmologist must check patients’ visual acuity to prevent irreversible blindness.