childhood parosteal osteosarcoma (Monarch Disease Ontology entry MONDO_0003654) is a low grade malignant bone-forming mesenchymal neoplasm arising from the surface of the bone. It occurs in childhood and usually affects the distal posterior femur, the proximal tibia, and proximal humerus. Painless swelling is the usual clinical sign. The prognosis is usually excellent. Also known as: childhood parosteal osteogenic sarcoma.