A rare congenital disorder of bone resorption is Malignant Infantile Osteopetrosis. It is caused by failure of osteoclasts to reabsorb immature bone. Malignant infantile osteopetrosis is present at birth or develops within the first few months of life. We are reporting a case of a child who presented to us with pain and swelling in left thigh. He was diagnosed as malignant infantile osteopetrosis with rickets, which is a rare paradoxical association.