Proptosis is a common yet cardinal symptom that may indicate the development of a wide range of diseases. Causes of proptosis are usually classified into vascular, inflammatory, endocrine, and neoplastic. Herein, the authors describe a case where proptosis manifested as the primary and only symptom of a massive brain arteriovenous malformation. Deprived of any other conventional symptoms and signs of a brain arteriovenous malformation, such as headaches, nausea, vision loss, increased ocular pressure, and so on, brain imaging played a key role in confirming the diagnosis of this patient. This case proclaims how imperative it is for ophthalmologists to consider the potential of brain arteriovenous malformation as a cause of proptosis and actively engage in brain imaging for diagnosis.