Local destruction of individual metastases by any of a number of effective modalities fails as a treatment for most patients with disseminated cancer because of the presence of either undetected micrometastases or simply too many lesions. The availability of a systemic therapy that could reduce the number of metastases to a manageable few would dramatically increase the utility of surgical metastasectomy or other locally ablative measures. Interleukin-2-based immunotherapy can serve exactly this function in some patients with renal cancer or melanoma. We review the effectiveness of surgery in treating limited relapses or residual disease in patients who have responded to systemic immunotherapy. These data indicate that a surprising percentage of such patients can enjoy durable disease-free survival after surgical removal of their oligometastases, and, for a significant minority, it appears to be curative.