The risk of malignant transformation of SO is generally low. Axial lesions as well as recurrent osteochondromas and MO seem to have an increased risk of malignant transformation. The follow-up, requiring sufficient primary diagnostics, includes regular self-control and can usually be clinically carried out in more peripherally located lesions but in certain cases supplementary X-ray imaging is needed. In cases of anatomical regions which are more difficult to access manually, follow-up examination by magnetic resonance imaging (MRI) is the method of choice. Especially MO patients seem to benefit from long-term follow-up: when the tumor is located in the trunk and in (proximal) long bones MRI or whole-body MRI, respectively, should be performed once a year after skeletal maturity because of the higher risk of malignant transformation in these patients.