Introduction: Vitamin D supplementation is an important clinical issue due to frequent deficiencies of this prohormone. In rare cases, however, its oversupply can lead to side-effects, such as hypercalcaemia. The following is a clinical case of a patient with diagnosed sarcoidosis who suffered from acute kidney injury in the course of hypercalcaemia due to an oversupply of vitamin 25(OH)D. The patient, after several measurements of vitamin 25(OH)D in the blood where its deficit was determined, started its supplementation. After several weeks, she began to suffer from different somatic afflictions: fatigue, headache, persistent constipation. In laboratory tests, acute kidney injury was determined. The patient was referred to the Nephrology Department where conservative treatment was introduced. During hospitalization, other causes of acute kidney injury and hyperkalcaemia were excluded. During the course of treatment, improvement in the patient’s condition was achieved. Also the parameters of serum creatinine and calcium level slowly decreased. Treatment for vitamin D deficiency is an extremely important issue in everyday medical work. However, it is important to consider possible side-effects of the drugs used, as well as specific recommendations for certain groups of patients. These include, among others, patients with granulomatous diseases, such as tuberculosis or sarcoidosis. Conclusions: Not all groups of patients should be given suplementation of vitamin D, but in patients receiving the supplementation, serum levels should be monitored.Calcium serum levels should be monitored