Fahr syndrome is a rare neurological condition characterized by idiopathic bilateral basal ganglia calcifications. It often presents psychiatric symptoms that may precede neurological signs, especially in adolescents, making early diagnosis a challenge. We report the case of a 17-year-old male who exhibited treatment-resistant psychotic symptoms including aggression, paranoia, and auditory hallucinations beginning at age 12. Extensive bilateral calcifications in the basal ganglia and subcortical regions were identified via cranial CT, with no evidence of metabolic or infectious etiology, confirming the diagnosis of idiopathic Fahr syndrome. Treatment with clozapine and brexpiprazole led to rapid and sustained symptom remission. This case emphasizes the importance of neuroimaging in adolescents with atypical psychiatric presentations and suggests that combined antipsychotic therapy may be effective in managing Fahr syndrome-related psychosis.