Autopsies. This study was conducted at a tertiary health care center. From 1990 to 2008, 26,560 medical autopsies were performed at this center, with an annual mean of 1,889. We examined the autopsies of the 4,710 (17.7%) patients in whom ARF was the cause of death. In 980 of these patients, the histological pulmonary findings could not be reviewed because the pulmonary tissue was not available (it was classified as ''without analysis''); histological pulmonary analyses were performed in the remaining 3,730 (79.2%) cases. In this study, we reviewed all of the available microscopic and macroscopic diagnoses of death at autopsy, along with the patient medical records. The only inclusion criterion for the definition of ARF was based on arterial blood gases (PaO2,60 mmHg or PaCO2.50 mmHg with pH,7.30) while breathing room air. [1] [2] [3] We excluded patients younger than one year of age and individuals not diagnosed with ARF.