Primary hyperparathyroidism is a disease with multisystemic and heterogeneous manifestations, characterized by underlying high parathormone concentrations. Despite neuropsychiatric involvement being one of the manifestations, psychosis is rare. This is the case of a 68-year-old female with a 10-day clinical course of anorexia, mutism, dysphagia, constipation, and weight loss. The patient had disorganized speech associated with paranoid delusions. Prior to this visit, the patient was recently diagnosed with a mixed anxiety-depressive disorder. For this reason, treatment with antidepressants in combination with atypical antipsychotics was administered without a satisfactory response. Neuroimaging, infectious panel, and toxicology screening showed no abnormal findings. Hypercalcemia secondary to a retropharyngeal ectopic parathyroid adenoma was the causative etiology of her primary hyperparathyroidism, and hypercalcemia treatment resolved the psychotic episode. We highlight the importance of recognizing psychosis as a possible initial presentation of hyperparathyroidism and hypercalcemia. Ruling out organic etiologies prior to diagnosing a primary cause of psychosis is crucial, as their treatment can reverse the psychotic symptoms.