Study objectives: To estimate the incidence of acute respiratory failure (ARF) in the United States and to analyze 31-day hospital mortality among a cohort of patients with ARF. Design and setting: Retrospective cohort drawn from the Nationwide Inpatient Sample of 6.4 million discharges from 904 representative nonfederal hospitals during 1994. Patients: All 61,223 patients in the sample whose discharge records indicated all of the following: acute respiratory distress or failure, mechanical ventilation, ≥ 24 h of hospitalization, and age ≥ 5 years. Results: An estimated 329,766 patients discharged from nonfederal hospitals nationwide in 1994 met study criteria for ARF. The incidence of ARF was 137.1 hospitalizations per 100,000 US residents age ≥ 5 years. Incidence increased nearly exponentially each decade until age 85 years. Overall, 35.9% of patients with ARF did not survive to hospital discharge. At 31 days, hospital mortality was 31.4%. According to the proportional hazards model, significant mortality hazards included age (≥ 80 years and ≥ 30 years), multiorgan system failure (MOSF), HIV, chronic liver disease, and cancer. Hospital admission for coronary artery bypass, drug overdose, or trauma other than head injury or burns was associated with a reduced mortality hazard. Interaction was present between age and MOSF, trauma, and cancer. A point system derived from the hazard model classified patients into seven groups with distinct 31-day survival probabilities ranging from 24 to 99%. Conclusions: The incidence of ARF increases markedly with age and is especially high among persons ≥ 65 years of age. Nonpulmonary hazards explain short-term (31-day) survival. [ABSTRACT FROM AUTHOR]