Reconstruction of defects occurring during periacetabular resections of pelvic tumors is required particularly in young and functionally active persons. Allograft reconstruction provides good functional outcomes in restoration of normal pelvic anatomy. A 24-year-old male patient was reconstructed with an allograft-prosthesis composite after periacetabular resection due to pelvic chondrosarcoma. After four years, a two-staged revision with a custom-made pelvic prosthesis was performed due to septic failure. Successful radiographic and functional outcomes were achieved at two-year follow-up. In conclusion, we suggest a two-staged revision with a custom-made pelvic prosthesis as a satisfactory option in case of septic failure of allograft reconstruction after periacetabular resection.