Recent studies have shown that psychiatric symptoms might be the only primary manifestation of central nervous system malignancy. As a result, clinicians might overlook a brain tumor diagnosis due to overlying psychiatric symptoms. We herein describe an adolescent female patient without tuberous sclerosis clinical features whose primary presentation for a subependymal giant-cell astrocytoma was restrictive eating disorder, urinary incontinence, and depression. The behavioral symptoms improved significantly following tumor resection. This case illustrates that compression of the frontal lobes and hypothalamus can manifest as primary psychiatric symptoms of subacutely manifested anhedonia, appetite loss, low energy, flat affect, and depressive mood. An absence of tuberous sclerosis clinical features should not preclude a diagnosis of subependymal giant-cell astrocytoma. Clinicians should maintain an index of suspicion for a brain tumor in patients with sudden-onset restrictive eating disorder and depression.