Meningiomas are common, usually benign intracranial tumors. They grow slowly and can remain asymptomatic for many years. Meningiomas can present as mental disorders rather than with neurologic signs or symptoms. In this case report we describe a middle-aged man with a 2-year history of depressive disorder who was diagnosed with a large olfactory fossa meningioma after he developed mental status changes and urinary incontinence. After the tumor was removed, the patient’s depressive symptoms resolved and his neurocognitive functions improved. We discuss the patient’s neuropsychological and psychiatric profiles to identify symptoms and other clues that could expedite identification of meningiomas in patients with psychiatric disorders. Because olfactory fossa meningiomas can present as depressive disorder, we recommend brain imaging to rule out organic brain lesions in middle-aged and older patients with new-onset psychiatric symptoms. Although tumor removal brought improvement of our patient’s mental state and neurocognitive functions, patients may not be able to recover their cognitive functions completely.