Metastatic renal cell carcinoma (RCC) is a disease that is resistant to conventional systemic therapy. Nonmyeloablative allogeneic stem cell transplant has activity in patients with metastatic RCC. This approach has been used in related donor transplantation but there are limited data on outcomes in the setting of unrelated donor (URD) transplantation. This phase II trial assessed the efficacy, safety, and responses in 16 patients, 10 related and 6 URD transplants after a reduced intensity conditioning regimen and stem cell transplant as a treatment for metastatic RCC. Sixteen patients received a conditioning consisting of either fludarabine, cyclophosphamide (n=11) or fludarabine, total body irradiation (n=5) followed by transplantation from an HLA-matched sibling donor or a unrelated HLA-donor. Cyclosporine and mycophenolate mofetil were administered as posttransplant immunosuppression. Patients were monitored for engraftment by short tandem repeat for myeloid and lymphoid lineages and clinical response was assessed by serial imaging. All patients achieved donor chimerism, 7 patients developed acute, grades 2 to 3, graft-versus-host disease. Chronic graft-versus-host disease occurred in 6 patients and transplant-related mortality was 12%. Of the 10 related donors, 1 obtained a complete response, 3 had a partial response, and 3 had stable disease. In the 6 patients who underwent URD transplant, 1 obtained a complete response and 1 patient had stable disease. These results suggest that similar outcomes are possible where either related or URD were used as the stem cell source in reduced intensity stem cell transplant for metastatic RCC.