Malignant Infantile Osteopetrosis (MIOP) is a rare genetic disorder due to osteoclast abnormal activity. We report a case of seven month-old female patient, diagnosed as MIOP while investigating the cause of hepatosplenomegaly associated with hydrocephalus.Systemic examination showed hepatosplenomegaly, growth failure and developmental milestones delay. Ophthalmic exam revealed bilateral optic atrophy.Chest radiography detected generalized dense bone. We report a rare ocular finding of primary optic atrophy in a rare case of malignant variety of osteopetrosis.The patient received supportive treatment. MIOP should be kept in mind as a rare cause of hepatosplenomegaly. Early diagnosis and timely Hematopoietic stem cell transplantation are the only curative approach for an otherwise fatal disease.