Acute respiratory failure (ARF) in patients with cancer is frequently a fatal event. To identify factors associated with survival of cancer patients admitted to an intensive care unit (ICU) for ARF, we conducted a prospective 5-year observational study in a medical ICU in a teaching hospital in Paris, France. The patients were 203 cancer patients with ARF mainly due to infectious pneumonia (58%), but also noninfectious pneumonia (9%), congestive heart failure (12%), and no identifiable cause (21%). We measured clinical characteristics and ICU and hospital mortality rates.ICU mortality was 44.8% and hospital mortality was 47.8%. Noninvasive mechanical ventilation was used in 79 (39%) patients and conventional mechanical ventilation in 114 (56%), the mortality rates being 48.1% and 75.4%, respectively. Among the 14 patients with late noninvasive mechanical ventilation failure (>48 hours), only 1 survived. The mortality rate was 100% in the 19 noncardiac patients in whom conventional mechanical ventilation was started after 72 hours. By multivariable analysis, factors associated with increased mortality were documented invasive aspergillosis (odds ratio [OR], 2.13; 95% confidence intervals [CI], 1.05-14.74), no definite diagnosis (OR, 3.85; 95% CI, 1.26-11.70), vasopressors (OR, 3.19; 95% CI, 1.28-7.95), first-line conventional mechanical ventilation (OR, 8.75; 95% CI, 2.35-35.24), conventional mechanical ventilation after noninvasive mechanical ventilation failure (OR, 17.46; 95% CI, 5.04-60.52), and late noninvasive mechanical ventilation failure (OR, 10.64; 95% CI, 1.05-107.83). Hospital mortality was lower in patients with cardiac pulmonary edema (OR, 0.16; 95% CI, 0.03-0.72). Survival gains achieved in critically ill cancer patients in recent years extend to patients requiring ventilatory assistance. The impact of conventional mechanical ventilation on survival depends on the time from ICU admission to conventional mechanical ventilation and on the patient's response to noninvasive mechanical ventilation.