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Little is known concerning erroneous surgical procedures of malignant bone tumors, and the prognostic effect of erroneous surgical procedures in osteosarcoma has not been determined.We retrospectively reviewed 240 patients with initially non-metastatic high-grade osteosarcoma of the pelvis and extremities and, of these, identified twenty-six who had undergone previous less appropriate surgical procedures due to misdiagnosis followed by adequate treatment at our institution. We evaluated the clinicopathologic characteristics of these twenty-six patients compared with the remaining 214 patients treated with regular protocol. Subsequently, thirty-eight patients (nineteen in the matched case group and nineteen in the matched control group) were matched for multiple different variables using propensity score matching, and the oncologic results in terms of event-free survival and overall survival were analyzed.The patients undergoing erroneous surgical procedures were typically older, with small, non-osteoblastic-type tumors that were in an unusual location, showed an osteolytic pattern on radiographs, had a tendency toward marginal or intralesional excision with positive histologic margin, and had not been treated with neoadjuvant chemotherapy (all p < 0.05). After adjustment of confounding variables by propensity score matching, there was no significant difference between matched groups with regard to event-free survival (p = 0.46) and overall survival (p = 0.99).Distinct differences existed in the clinicopathologic characteristics of the patients who underwent erroneous surgical procedures due to misdiagnosis. We failed to detect a prognostic relevance of the presence of previous erroneous procedures followed by adequate treatment.Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.