BACKGROUND: Long bone pathologic fractures, especially when radiation-induced, represent a significant and difficult-to-treat entity. The ultimate goal of treatment is limb salvage; however, there are no treatment methods that guarantee bony healing. The vascularized fibula flap has revolutionized bone reconstruction, including that of the long bones. The authors report the results of onlay vascularized fibula flaps for pathologic long bone fractures and the outcomes and complications of this reconstruction method. METHODS: Records of patients who underwent long bone pathologic fracture reconstruction with the vascularized fibula onlay flap were reviewed retrospectively. Records were analyzed for reconstruction details, time to bony union, subsequent operations, clinical and functional outcomes, and complications associated with harvest and reconstruction. RESULTS: Twenty-five patients met the study criteria. Twenty-one patients demonstrated bony fracture union at an average of 11 months after fibular flap onlay grafting. Two patients who had experienced bony union ultimately required amputations for reasons unrelated to reconstruction. All four patients whose fibular flap failed later obtained limb salvage after further procedures. Thirteen of 25 patients achieved a good or excellent functional outcome as judged by a common oncologic reconstruction functional outcome scale. Postsurgical complications were common in this patient group, with a total of 22 distinct complications (88 percent incidence). CONCLUSIONS: Despite a high complication rate, this study demonstrates that pathologic long bone fracture salvage with an onlay fibula flap achieves relatively good clinical and functional outcomes. Limb salvage was made possible in a majority of patients, all of whom experienced a difficult problem in the form of long bone pathologic fractures.