Introduction: Parosteal osteosarcoma is a rare, mostly low grade tumor arising from the surface of the bone. The aim of the study was to establish risk factors for local recurrence (LR) and death.

Method: Retrospective review of a prospectively collected database with complete up-to-date follow up.

Results: 63 patients were diagnosed and treated at our centre from 1978 to 2007. The most common site was the femur (37) followed by the tibia (10) and humerus (9). The median size was 7cm (2 – 16). At the time of diagnosis 27 (43%) were low grade, 13 (21%) were low grade but had invaded the medullary canal and 8 (13%) had a high grade component; the data was missing in 15 patients (24%). All patients were operated.

LR arose in 11 patients (17.5%) at a mean of 38 months and was related to surgical margins. There were no LR in the 26 wide resections, but the risk of LR was 20% in those with a marginal and 46% in those with an intralesional excision. LR appeared as a higher grade than the primary tumor in 3 patients (27%).

9 (14.3%) patients developed metastases at a median of 22 months (6 – 123). Five patients developed both LR and metastases. Seven patients died from the tumor, 2 patients are alive with metastatic disease.

None of the patients with a low grade tumor and wide or marginal margins died of tumor, but 2 patients (18%) operated intralesional died of tumor.

Discussion: There was a statistically significant relationship between surgical margins and LR (p< 0.001). All patients with low grade parosteal osteosarcoma operated with wide margins have been cured. LR appeared often in higher grade than the primary tumor. Patients with low grade tumor and intralesional margins had 18% risk to tumor-ralated death.