Nderwent reconstruction with a modular prosthesis (twelve total humeral replacements and forty-one distal humeral replacements) after tumor resection (thirty-eight elbows) or because of massive joint degeneration (fifteen elbows). In the tumor group, twenty-three patients (twenty-four elbows) had metastatic disease and fourteen had a primary tumor. Degenerative defects of the distal end of the humerus were caused by pseudarthrosis (six elbows), prosthetic failure (five), trauma (two), osteomyelitis (one), and supracondylar fracture (one). The mean duration of follow-up for all patients was twenty-eight months (median, thirteen months; range, one to 219 months). Results: The mean Inglis-Pellicci score in the tumor group was 84 points, and the mean Musculoskeletal Tumor Society score was 78%. Patients with total humeral reconstruction had worse scores than those with distal humeral reconstruction. Twenty-four patients died of disease at a mean of thirteen months after surgery. Local tumor control was achieved in all patients. In the revision group, the mean Inglis-Pellicci score was 76 points. The Inglis-Pellicci score was significantly better for patients in the tumor group. Eight patients (15%) had a deep periprosthetic infection, requiring amputation in one patient (2%) and prosthetic removal in two patients (4%). Four patients (8%) had the implants revised for aseptic loosening. Conclusions: Modular prostheses of the distal end of the humerus provide a stable reconstruction of the elbow with satisfactory function and disease control in patients with a tumor, but careful patient selection is required when the prostheses are used for revision surgery in patients without a tumor. Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence....