Three patients, two women aged 79 and 80 and a man aged 84, showed symptoms of cognitive impairment caused by primary hyperparathyroidism. Parathyroidectomy lead to a marked improvement in the symptoms. The incidence of primary hyperparathyroidism increases with age. Most patients only show slight symptoms. In addition, clinical symptoms in elderly patients differ from those in younger patients with mental changes, general tiredness and reduced muscular strength being prevalent. In accordance with the literature, which shows high cure rates with low morbidity and mortality, we recommend that parathyroid surgery be considered in elderly patients who exhibit only slight or mental symptoms of primary hyperparathyroidism.