Introduction: This study is aimed to assess the functional results of cases with lower extremity malignant and metastatic bone tumours that were treated with modular tumour resection prostheses. Materials and Methods: 49 patients were retrospectively examined. 27 (55.1%) patients had a primary bone tumour, and 22 (44.9%) had a metastatic bone tumour. Although most tumours located in the proximal femur were metastatic, tumours located around the knee were mostly primary malignant bone tumours. The functional assessments of our patients were made according to the Musculoskeletal Tumour Society (MSTS) scoring system. The Student's t-test and the Chi-square test were used for statistical analyses. Results: 30 (61.2%) of the patients were men, and 19 (38.8%) were women. The average age was 46.2 +/- 1.9 years. Tumours were located in the proximal femur in 27 (55.1%) patients, distal femur in 16 (32.7%) patients and proximal tibia in 6 (12.2%) patients. 14 (28.6%) patients had a pathological fracture on admission. The average follow-up period of our patients was 27.4 +/- 3.4 months, and the average MSTS score was 74.3 +/- 13%. Complications developed at any time in 34.7% of the patients, and the most common symptoms were aseptic loosening (8.2%) and prosthesis infection (8.2%). Local relapse was found in one (2%) patient. The 5-year survival rate was 68.3% in patients with a primary tumour and 30% in patients with a metastatic tumour. Conclusion: Although endoprosthesis reconstruction had advantages of giving very good functional results in the early phases, it was found to cause mechanical complications, especially in patients with primary bone tumours during the mid and late phases.