The authors retrospectively evaluated the clinical records and radiographs of 20 patients with a variety of neoplasms in the long bones treated with local resection and allograft replacement. All of the tumors were peridiaphyseal and required an interposed (intercalary) segmental allograft replacement. Postoperative complications developed in 40% of the patients. However, the eventual clinical outcome was good or excellent in 85% of all cases. Various factors appeared to be responsible for the development of complications or the eventual clinical outcome, including union of the graft with the host tissue, soft-tissue swelling, callus formation, and type of allograft (hemi or full). Knowledge of these factors and the relationship between complications and radiographic findings may lead to an early diagnosis and appropriate treatment.