Brain tumors may present themselves initially under the appearance of depression, anxiety, psychosis, apathy, personality change, or cognitive decline, and psychiatric comorbidity remains frequent throughout the course of the neuro-oncological disease. In this Perspective, we argue that psychiatric expertise should be embedded in neuro-oncology care from the patient's first presentation through survivorship and palliation. We draw on the literature and on two cases from our liaison psychiatry service, in which older adults referred for depressive symptoms were found to have intracranial tumors and continued to need psychotropic treatment after successful surgery. We compare how DSM-5-TR and ICD-11 classify psychiatric syndromes secondary to brain disease and propose a four-domain etiological formulation that separates direct tumor effects, treatment-related and endocrine effects, psychological reactions, and pre-existing vulnerability. This article also presents the most relevant red flags that should prompt neuroimaging, the distinction between apathy and depression, the burden of depression, distress, suicide risk, and postoperative delirium, and the psychiatric effects of corticosteroids, antiseizure medications, dopamine agonists, and cranial irradiation. We also address practical psychopharmacology, electroconvulsive therapy, decision-making capacity, cognitive rehabilitation, and mood assessment in aphasia, while highlighting the scarcity of controlled evidence in this population. Finally, a phase-based, multidisciplinary model of care is proposed, and an outline of research priorities is presented.