Critically ill cancer patients constitute a large percentage of admissions to tertiary care medical intensive care units (ICUs). We sought to describe outcomes of such patients, and to evaluate how conditions commonly seen in these patients impact mortality. A total of 348 consecutive medical ICU cancer patients were evaluated. Subgroup comparisons included the three most common cancer types (leukemia, lymphoma, lung cancer), as well as three different treatments/conditions (bone marrow transplant [BMT] versus non-BMT, mechanical ventilation [MV] versus non-MV, neutropenic versus non-neutropenic). There were no mortality differences between patients with leukemia, lymphoma, or lung cancer. By logistic regression, mortality predictors were: MV, hepatic failure, and cardiovascular failure for the group as a whole (41% overall mortality); MV and allogeneic (as compared with autologous) BMT for the BMT group (39% overall mortality); hepatic failure, cardiovascular failure, and persistent acute respiratory distress syndrome (ARDS) for the MV group (67% overall mortality); and MV for the neutropenic group (53% overall mortality). Neutropenia showed no independent association with mortality in the group as a whole or any subgroup analyzed. We conclude that respiratory, hepatic, and cardiovascular failure predict mortality, whereas neutropenia does not. Additionally, we have noted an encouraging improvement in survival in many groups of critically ill cancer patients.