High-dose interleukin-2 (IL-2) results in objective clinical regression of metastatic cancer in 15% to 17% of patients with melanoma and renal cell carcinoma. Durable complete regression of all metastases is seen in 6% to 8% of patients. Based on these findings, the U.S. Food and Drug Administration has approved the use of high-dose IL-2 for the treatment of patients with metastatic melanoma and renal cell carcinoma. Interleukin-2 administration is associated with many different side effects, and after many years of use, clinicians have learned how to safely administer high-dose IL-2. This article details practical guidelines for the safe administration of high-dose IL-2.