Impaired calcium and vitamin D homeostasis in the elderly results in (senile) secondary hyperparathyroidism and increased bone resorption leading to increased fracture risk. We have investigated the prevalence of secondary hyperparathyroidism in 201 patients aged 80 years or over in a hospital medical department. Patients with illnesses or treatment influencing calcium and vitamin D homeostasis were excluded. 168 patients, 107 women (age 81-97, median 86) and 61 men (age 80-94, median 85) were included. Thirty-five percent (38/107) of the women and 25% (15/61) of the men had parathyroid hormone values above the upper reference limit, 6.9 pmol/L. In conclusion, (senile) secondary hyperparathyroidism is frequent in elderly patients in a general medical department. The findings demonstrate the importance of giving the elderly calcium and vitamin D supplements.