Hypervitaminosis D occurs in infants due to increased intake of vitamin D and results in hypercalcemia and hypercalciuria. We present the case of a 4.5-month old infant with signs of vitamin D intoxication, which occurred due to supplementation for the purpose of rickets prevention and diet with vitamin D-fortified milk. The clinical manifestations were constipation, vomiting and failure to thrive. After excluding hormonal, tumoral and malformative (Williams syndrome) causes, treatment included hyperhydration, loop diuretics and prednisone. This case highlights the need for proper informing of parents on the manners of vitamin D supplementation during the first year of life in order to avoid dangers of parental dosing errors.