A rare cause of a relatively common neonatal emergency.

Malignant infantile osteopetrosis (MIOP) is a rare cause in the list of etiological factors of neonatal hypocalcemia in several textbooks. The most severe complication of MIOP is bone marrow suppression. The abnormal expansion of bone interferes with medullary haematopoiesis. Most children with this disease die within the first decade of life of secondary consequence of bone marrow failure. Hematopoietic stem cell transplantation (HSCT) is the only curative therapy for MIOP, an otherwise fatal disease. We present a neonate with MIOP that was further complicated with vitamin D deficiency.