The authors report four cases of hypercalcemia occurring during the course of carcinoma of the prostate. This association is rare (less than twenty published cases) though not exceptional, carcinoma of the prostate accounting for almost 4 per cent of causes of malignant hypercalcemia. This generally involves advanced and metastatic forms, at the terminal phase, but cases of regression after hormone therapy have been reported. The histological type of the tumour is unusual in one case in two (anaplastic or carcinoid). The mechanism of this hypercalcemia is humoral, probably by secretion of a parathormone-like peptide, but which has not yet been fully elucidated.