Vitamin D (calciferol), is a fat-soluble vitamin and it is contained in very few foods. The main source of this vitamin is skin production. Subclinical vitamin D deficiency, diagnosed by a low 25 hydroxy vitamin D level, is a very common disorder. The first step in the evaluation of a patient with hypercalcemia is to verify the condition with a repeat measurement. After that, differential diagnosis of parathormone (PTH) mediated and non PTH mediated hypercalcemia should be performed by the measurement of PTH. A 71-year-old female patient presented to the hospital with a history of nausea, loss of appetite, and confusion for 1 week. Hypercalcemia and acute kidney injury, linked to oral vitamin D replacement, were detected. Vitamin D has many important effects on various systems and paying attention to the total replacement dosage is as important as treating the deficiency itself.