ABSTRACT
Osteoblastic osteosarcoma is the most frequent malignant bone neoplasia in pediatric patients. It accounts for 50% of primary bone tumors and the most frequent age at presentation is adolescence, particularly during the growth spurts. Cases of children younger than 8 years of age have been reported in the literature. The purpose of this article is to report the case of a male, 19 month-old patient with osteoblastic osteosarcoma of the left distal femur and proximal tibia. It is considered as a special case due both to the age at presentation and to the multicenter feature of the tumor. This suggests that this entity may be more aggressive and rapidly growing in younger children. At the National Pediatrics Institute, in 35 years we only had three cases of children younger than 5 years.