Myelofibrosis is a rare disorder in childhood. In this report, we present the case of a 6-month-old infant with myelofibrosis due to severe vitamin D deficiency rickets. The characteristic clinical and laboratory findings of myelofibrosis improved rapidly after vitamin D therapy. In developing countries, nutritional rickets is still an important health problem. Rickets is not only a skeletal system-related disorder, it is also a systemic disorder. Rickets should be considered, therefore, as one of the conditions that can lead to severe haematological disorders in infants.