Interleukin 2, has frequent and important side effects. Toxic effects observed are systemic (fever, chills, malaise), hemodynamic (capillary leak syndrome, hypotension), cardiac (arrhythmia, infarction), renal (renal dysfunction), infectious (septicemia), cutaneous, hematologic, gastrointestinal, endocrinologic and metabolic. Side effects are dose-dependent, generally reversible, with a mortality from 1 to 3%. Regimens of administration and other cytokine combinations affect interleukin 2 toxicity. If the treatment of these side effects is well known, selection of patients and specialized care unit remain always necessary.