A prospective survey was carried out to determine the incidence of hypercalcemia in hospitalized patients with lymphoma. Serum calcium determinations were carried out during 440 admissions on 152 patients, most of whom had widespread lymphoma. Forty-one of the 152 patients died, all having had calcium levels recorded on that admission. Two of the 152 patients (1.3%) were found to have hypercalcemia. By comparison hypercalcemia occurred in 6 of 34 patients (17.6%) with multiple myeloma.Hypercalcemia is uncommonly associated with lymphoma but may be seen particularly in centres where many patients with this disease are treated. Hypercalcemia readily responds to therapy and is a reversible cause of morbidity, but when associated with lymphoma it usually indicates widespread disease. The mechanism of hypercalcemia is unknown but there is strong evidence for humoral factors that may or may not be related to parathyroid hormone.