Osteopetrosis means a low function of osteoclasts, that induces bone resorption with a decrease in bone density. It has two genetic forms: a benign form with autosomal dominant inheritance (AD) and a malignant form with autosomal recessive inheritance (AR). The most successful therapy is bone marrow transplantation (rate of success 80%). We will present a case of malignant osteopetrosis of a five years old child. The late diagnosis (at 18 month) and the malignant evolution has made possible only palliative treatment, without surgical or ophthalmologic-neurosurgical implication. The prognosis is unfavorable with 70% survival to six years and 30% to ten years.