Hypercalcemia in children is a medical emergency and often manifests as nonspecific symptoms such as nausea, vomiting, weight loss, and anorexia. Severe hypercalcemia is a rare complication of malignancy in children, while it can be seen in various types of malignant tumors. It is usually associated with significant morbidity and may be severe enough to threaten life. Incidence of hypercalcemia in hematopoietic malignancies including acute lymphoblastic leukemia (ALL) is very rare and unusual, especially as the initial manifestation of the disease. In this paper a 6-year-old boy who had severe hypercalcemia and gastrointestinal symptoms before the onset of common and usual manifestations of ALL is introduced.