It is important to identify the cause of hypercalcaemia to give the best possible treatment. The primary treatment is to remove the underlying cause and rehydration. When the parathyroid hormone (PTH) level is elevated the most common causes are primary hyperparathyroidism and thiazides. The treatment is operation and discontinuation of the medicine. Cinacalcet can be used to lower the serum calcium level preoperatively. When the PTH level is low the most common causes are dehydration, malignant disease and treatment with calcium. The hypercalcaemia in malignant disease can be treated with prednisone, bisphosphonates and denosumab.