A five-year experience with ten cases of primary resection of aggressive bone lesions treated by immediate reconstruction with autologous fibula demonstrates the advantages of vascularized, compared with free bone, graft. The procedure was performed for locally aggressive bone tumors in seven cases, and for Type III congenital pseudarthroses of the tibia in three cases. In large intercalary bone grafts, the vascularized fibula actively participates in the healing process, rather than serving merely as a framework for inductive creeping substitution, as is the case in conventional bone grafts. With the exception of one case, the grafts united and progressively hypertrophied, and there was no tumor recurrence. For defects less than 6 cm in diameter, conventional bone grafts usually prove successful. However, for defects greater than 6 cm or in a poorly vascularized bed, the vascularized fibular graft can prevent such complications as fatigue fracture, failure of incorporation, and nonunion that are frequently seen with nonvascularized cortical and cancellous bone grafts.