The introduction of new treatments for cancer and advances in intensive care for critically ill patients with cancer have improved prognosis and survival. This article reviews the main reasons for admission to the intensive care unit, the criteria for admission, the role played by early intensive care unit admission and predictors of mortality in critically ill patients with cancer. The primary reasons for admission of cancer patients to the intensive care unit are medical/surgical problems that arise or are exacerbated during antineoplastic treatments such as acute respiratory failure, sepsis, multiple organ failure, and oncologic emergencies. As the main prognostic factor in critically ill patients with cancer is the number and severity of organ failures, early admission to the intensive care unit with the lowest possible number of organ failures is recommended. Survival rates for cancer patients who are admitted to the intensive care unit have improved, so admission should not be denied to patients only on the basis that the patient has cancer. At present, treatment of these patients represents a challenge for the oncologist, hematologist, surgical oncologist, and critical care specialist. Our working group recommends early admission to the intensive care unit for cancer patients who have the lowest possible number of failing organs.