Pelvic reconstruction with conventional 3D-printed prostheses faces a critical trade-off, where achieving sufficient porosity for optimal bone ingrowth often compromises essential mechanical stability. To address this challenge, this study evaluates the clinical outcomes of 3D-printed hemipelvic prostheses incorporating re-entrant chiral structure (RCS), a novel negative Poisson's ratio design, in patients undergoing pelvic reconstruction following tumor resection.A retrospective analysis was conducted on 15 patients (eight females and seven males; mean age: 39.3 ± 11.7 years) with pelvic malignancies who underwent reconstruction using 3D-printed hemipelvic prostheses incorporating RCS between March 2018 and June 2023. The diagnoses included osteosarcoma (n = 8), Ewing's sarcoma (n = 3), chondrosarcoma (n = 2), and high-grade soft tissue sarcoma (n = 2). All patients were staged as IIB according to the Enneking system, except for one case of Ewing's sarcoma (stage III). Neoadjuvant chemotherapy (four cycles) was administered to six osteosarcoma patients, and one Ewing's sarcoma patient received six cycles, while other patients proceeded directly to surgery. Patient outcomes were systematically evaluated through oncological status, functional performance (MSTS-93 score), pain assessment (VAS score), surgical parameters, complications, and radiographic analysis using Tomosynthesis Shimadzu Metal Artifact Reduction Technology (T-SMART).At the latest follow-up (44.5 ± 9.4 months), 13 patients (86.7%) remained disease-free; one patient (6.7%) experienced local recurrence requiring revision surgery, and one patient (6.7%) died of metastatic complications at 32 months post-surgery. Functional outcomes showed significant improvement, with mean MSTS-93 scores increasing from 14.5 ± 1.1 preoperatively to 25.8 ± 1.3 at final follow-up (p < 0.001). Pain control was satisfactory, with VAS scores decreasing from 5.5 ± 0.6 to 1.5 ± 0.5 (p < 0.001). The mean surgical duration was 289.3 ± 30.4 min, with an average intraoperative blood loss of 3540 ± 621.5 mL. Early complications included delayed wound healing in three cases (20%), successfully managed with wound care protocols and VAC therapy. One patient (6.7%) developed deep prosthetic infection at 14 months post-surgery, necessitating a two-stage revision procedure. No mechanical failures, aseptic loosening, or prosthesis fractures were observed during the follow-up period. Radiographic analysis demonstrated progressive bone ingrowth into the RCS porous regions in all cases, with no signs of osteolysis or implant migration in the remaining prostheses.D-printed custom hemipelvic prostheses with RCS offer an effective solution for pelvic reconstruction by achieving an optimal balance between mechanical stability and biological integration, leading to promising clinical outcomes.© 2025 The Author(s). Orthopaedic Surgery published by Tianjin Hospital and John Wiley & Sons Australia, Ltd.