Purpose: To evaluate the outcomes of critically ill patients with cancer and acute renal dysfunction. Patients and Methods: Prospective cohort study conducted at a 10-bed oncologic medical-surgical intensive care unit (ICU) over a 56-month period. Results: Of 975 patients, 309 (32%) had renal dysfunction and were studied. Their mean age was 60.9 ± 15.9 years; 233 patients (75%) had solid tumors and 76 (25%) had hematologic malignancies. During the ICU stay, 98 patients (32%) received dialysis. Renal dysfunction was multifactorial in 56% of the patients, and the main associated factors were shock/ischemia (72%) and sepsis (63%). Overall hospital and 6-month mortality rates were 64% and 73%, respectively. Among patients who required dialysis, mortality rates were lower in patients who received dialysis on the first day of ICU in comparison with those who required it thereafter. In a multivariable Cox model, age more than 60 years, uncontrolled cancer, impaired performance status, and more than two associated organ failures were associated with increased 6-month mortality. Renal function was completely re-established in 82% and partially re-established in 12%, and only 6% of survivors required chronic dialysis. Conclusion: Acute renal dysfunction is frequent in critically ill patients with cancer. Although mortality rates are high, selected patients can benefit from ICU care and advanced organ support. When evaluating prognosis and the appropriateness of dialysis in these patients, older age, functional capacity, cancer status and the severity of associated organ failures are important variables to take into consideration.