Thirty-nine patients who had a malignant or an aggressive benign bone tumor about the knee were managed with a resection arthrodesis with use of an intercalary allograft fixed with an intramedullary nail. In thirty-one patients, this was the method chosen for the initial reconstruction after resection of the tumor. In eight patients, another type of reconstruction had already failed. Both the proximal and the distal allograft-host junction healed and the functional outcome was satisfactory in thirty-two patients. Non-union developed in seven patients: at one junction in six patients and at both junctions in one. In five patients, the non-union healed after bone-grafting, repeat internal fixation, or replacement of the allograft. An above-the-knee amputation was done for two patients, both of whom had had a chronic non-union. One patient had a local recurrence, and it was treated with an above-the-knee amputation.