Malignant infantile osteopetrosis presents in the first months of life with hepatosplenomegaly, anemia, thrombocytopenia, optic atrophy, and deafness. It may rarely present with rickets. Here, we present a boy who had osteopetrosis coexisting with rickets. A four-month-old boy was consulted to our clinic due to hepatosplenomegaly. He was the first child of consanguineous parents. He was diagnosed as rickets at the age of 2.5 months. Laboratory investigation revealed anemia, leukocytosis and thrombocytopenia, as well as hypocalcemia (5.4 mg/dl), phosphorus 4.2 mg/dl, and increased alkaline phosphatase (1411 IU/L). Parathormone level was high (112 pg/ml), and urine Ca/Cre was low (0.07). Bone X-rays revealed generalized increased bone density and widening and cupping of the distal epiphyses of the radius and ulna. The findings were compatible with osteopetrosis and rickets. Vitamin D (2000 IU/d po) was given for a one-week period with calcium gluconate, and then 400 IU vitamin D was continued daily. In conclusion, rickets may be the first finding in osteopetrosis. We suggest that physicians should give effort to determine if rickets is present in a baby with osteopetrosis, and if a baby with rickets is unresponsive to appropriate therapy or rickets is recurrent, the differential diagnosis should include osteopetrosis.