| - Internal hemipelvectomy may be indicated in the treatment of select tumors of the pelvis and lower extremity, and has become our preferred approach due to favorable outcomes. After such extensive resections, which can involve long operative times and significant blood loss, there are often substantial bony and soft tissue deficits. However, it is unclear whether the benefits of reconstruction in these cases outweigh the risks involved. In the largest series to date of internal hemipelvectomy patients, we evaluate the effect of reconstruction on surgical complications, postoperative function, and survival. A retrospective review was performed of all patients who underwent internal hemipelvectomy between 1998 and 2011. Outcomes for patients who underwent reconstruction were compared to outcomes for those who did not. A total of 111 patients underwent internal hemipelvectomy, of which 51 (45.9%) received reconstruction and 60 (54.1%) did not. In cases of reconstruction, 30 (58.8%) involved placement of mesh for abdominal wall and pelvic floor reconstruction, 27 (52.9%) involved a soft tissue flap, and 15 (29.4%) involved a vascularized bone flap to restore pelvic ring continuity. Two concurrent reconstructive procedures were performed in 22 (43.1%) patients. The overall rate of early complications was 19.8%, which occurred in 15.7% of patients who received reconstruction compared to 23.3% in patients who did not (P = 0.35). Late recipient-site complications occurred significantly less often in patients who underwent reconstruction (7.8% vs 26.7%, respectively; P = 0.01). From a functional standpoint, Musculoskeletal Tumor Society scores were higher in patients who underwent reconstruction, although this was not statistically significant (62.8% vs 48.4%, respectively; P = 0.12). The 2 groups were similar with regard to operative time, blood loss, and hospital stay, as well as overall and disease-free survival rates. Overall, these results indicate that immediate reconstruction of internal hemipelvectomy defects significantly reduces the incidence of late recipient-site complications, without an adverse effect on perioperative course or overall function. An algorithm for reconstruction based on these outcomes is presented.