Mental manifestations of primary hyperparathyroidism simulate a wide spectrum of psychiatric disorders. Definitive surgical treatment results in long-lasting full recovery. The 2 cases presented demonstrate this. The clinical diagnostic and therapeutic aspects of primary hyperparathyroidism, with an emphasis on neuropsychiatric manifestations, are discussed. Early diagnosis of hypercalcemia can prevent unnecessary and potentially harmful treatment with antidepressive, anxiolytic or antipsychotic drugs, which can further depress the cognitive state of the patients, and can aggravate the mental symptoms.