We report a postmenopausal woman with primary hyperparathyroidism (PHPT) and severe hypercalcemia while her total calcium intake was more than 2 g daily. Despite a markedly elevated intact PTH level, her serum 1,25-dihydroxyvitamin D [1,25-(OH)2D] level was low (17 pmol/L; 7 pg/mL). With reduced calcium intake, her serum calcium normalized, and 1,25-(OH)2D increased to 122 pmol/L (51 pg/mL). At the same time, intact PTH decreased to 32% of the initial value. PHPT may be associated with low circulating 1,25-(OH)2D levels. Furthermore, low 1,25-(OH)2D levels in PHPT may be due to a direct effect of severe hypercalcemia and be reversible with correction of hypercalcemia.