Objectives: This study aims to evaluate functional outcomes ofpatients and to analyze complication rates of modular intercalaryendoprosthetic reconstruction after resection of metastaticdiaphyseal bone lesions. Patients and methods: Between December 2017 and February2020, 22 patients (15 males, 7 females; median age: 64.2years; range, 49 to 91) who underwent reconstruction withmodular intercalary endoprostheses for metastatic bone tumorsat five different centers were retrospectively analyzed. Age, sex,diagnosis, follow-up duration, previous treatments of patients,and resection lengths were recorded. The Musculoskeletal TumorSociety Scores (MSTS) were used to assess functional status ofavailable patients at the final follow-up. Failures were categorizedaccording to the Henderson classification. Results: Locations of the resected tumors included 10 humeri(45.5%), five tibiae (22.7%), and seven femurs (31.8%). Thelength of the resected tissues ranged from 35 mm to 180 mm.Seven patients (31.8%) died of disease, and one patient died ofpneumonia within follow-up period. The functional outcomesof surviving patients were satisfying with a median MSTSscore of 86.9% (range, 70 to 100%) at a median follow-up of17 (range, 8 to 26) months. There were two cases of type II (9%),one cases of type IIIa (4.5%), two cases of type IIIb (9%), andone case of type IV (4.5%) failure. Complications were mostcommonly observed in tibial reconstructions. Conclusion: The good short-term functional results wereachieved in surviving patients. Uncomplicated patients wereable to perform daily living activities without limitations. Theoverall rate of complications was relatively low and, among them,mechanical problems were the most commonly encounteredproblems.