Fifteen cases of a recently described variety of osteosarcoma, periosteal osteosarcoma, were studied to define their radiographic characteristics. All the lesions were limited to the cortex that was always thickened but without invasion of the medulla cavity. The tumors presented as non-homogeneous masses of spiculated osteoid matrix progressively denser from the periphery to their cortical base. The average age was 28 and the most common location was the proximal third of the femur; all the lesions were diaphyseal in location. The spectrum of radiographic features and differential diagnosis are described in detail.