Humoral hypercalcaemia of malignancy (HHM) is defined by a tumor producing hypercalcemia through a systemic hormone or cytokine. In approximately 80% of HHM cases, parathyroid hormone-related peptide (PTHrP) is the causal factor. Primary hyperparathyroidism (PHPT) and metastasis to the bone are the most important differential diagnoses. The treatment strategy in cases of HHM is to decrease the serum calcium by fluid, loop diuretics, glucorticoids and bisphosphonate. Moreover, the underlying malignant disease should be treated. The prognosis for patients with HHM, however, is poor.