Background. The purpose of this work was to study clinical and histopathological tumor characteristics of patients treated for synchronous or metachronous skeletal osteosarcoma at The Norwegian Radium Hospital from January 1, 1980 to January 1, 2008. Patients and methods. The hospital sarcoma database and patient records were reviewed to identify cases with synchronous or metachronous skeletal osteosarcoma. Patients with more than one skeletal lesion in the absence of pulmonary or other soft tissue tumor manifestations were included in the study, and histopathological slides from these tumors were reviewed. Results. Among a total of 297 registered osteosarcoma patients, six with synchronous (2.0%) and 10 with metachronous (3.4%) skeletal osteosarcomas were identified. All tumors were of high-grade malignancy. Treatment at the time of the first osteosarcoma diagnosis was in most cases wide resections and multi-agent chemotherapy according to international protocols, whereas the treatment for metachronous tumors was individualized and in general much less intensive. One patient was diagnosed with Li-Fraumeni syndrome, two other individuals may be suspected to have the same syndrome, and yet another patient had previously been treated for a bilateral retinoblastoma. Thirteen patients are dead, 11 from metastatic osteosarcoma, one from myelodysplastic syndrome, and one from wound infection and methotrexate-related nephrotoxicity; whereas three patients are still alive with no evidence of osteosarcoma. Conclusions. The prognosis for patients with synchronous and metachronous skeletal osteosarcoma is poor. However, because long-term survival is seen, aggressive treatment to selected cases, e.g., patients with an osteosarcoma predisposing syndrome and/or late occurring metachronous tumours, is justified. Revealing a possible clonal relationship between these tumors, e.g., by karyotyping, may be of interest for estimating prognosis and guide therapy intensiveness.