BACKGROUND: Hypercalcaemia of malignancy, a relatively frequent phenomenon, seems to be insufficiently recognized and treated. Its symptoms are not specific, but they affect the quality of life. METHODS: A prospective study to analyse the influence of symptoms caused by hypercalcaemia on the decision of the admitting physician, the motivation for treatment, and the effect of the treatment on the given symptoms in hospitalized patients with oncologic disease in progression, where confounding causes of similar symptoms such as cerebral metastasis, radiotherapy, treatment with opioids, etc., were excluded. RESULTS: A total of 71 patients, mean age 65 + 11 years, fulfilled the strict inclusion criteria. About 42% were hospitalized because of symptoms caused by hypercalcaemia, but none of the medical reports mentioned hypercalcaemia as reason for hospitalization. Specific antihypercalcaemic therapy was given to only 37% of patients, and only 25% got an adequate rehydratation. Antihypercalcaemic treatment was guided by the severity of hypercalcaemia (>3.00 mmol L(-1)), not by the symptoms. Polyuria-polydipsia, nausea-vomiting and constipation were correlated with hypercalcaemia. These symptoms, as well as confusion-stupor and bone pains improved significantly when calcaemia was normalized. Patients with calcaemia normalized returned home most frequently (P < 0.03). CONCLUSIONS: Malignant hypercalcaemia remains mostly undiagnosed in medical praxis. Specific treatment occurs in too small fractions of the patients. As the normalization of calcaemia significantly improves the symptoms because of hypercalcaemia and the quality of life, rapid rehydration and specific calcium lowering treatments should be part of palliative measures in all patients with malignant hypercalcaemia.