Primary sarcoma of bone is a rare entity but nevertheless a significant cause of mortality in children and adolescents. The focus of the preoperative evaluation is to set up a histological diagnosis, define local tumor extent and develop a therapy regimen. In addition to patient history and clinical findings a radiograph in two orthogonal planes is still of great importance. MRI plays a major role in the further clarification of the diagnosis, while CT is valuable in the diagnosis of tumors of the axial skeleton as well as in systemic staging. A PET-CT can be performed to obtain an overview of further tumor sites. Open bone biopsy is the final diagnostic step and should be carried out at the institution where the definitive treatment will be performed. Complications such as fracture, neural lesions and spread of tumor cells are relatively rare if the biopsy is performed appropriately; however, patients should be instructed to strictly avoid weight-bearing on the affected extremity.