['To determine whether extreme obesity (morbid obesity; body mass index > or =40 kg/m(2)) is an independent risk factor for death among critically ill patients; this objective is most salient in the subset of patients who sustain a prolonged intensive care unit stay during which the burdens of care imposed by obesity and its consequences would become most apparent.', 'Cohort analysis of data from the Project Impact database used to catalog admissions and outcomes to a surgical intensive care unit, with predetermined end point analyses of outcomes.', 'Surgical intensive care unit serving Tufts-New England Medical Center, a tertiary care and university medical center in Boston.', 'All critically ill surgical patients admitted to the Tufts-New England Medical Center surgical intensive care unit from January 1998 to March 2001.', 'Intensive care unit and hospital mortality and lengths of stay were compared with body mass index subclassified into five groups: underweight, normal weight, overweight, obese, and extremely obese. Data were examined for all admissions during the study period and for a predetermined subgroup with a prolonged intensive care unit stay (> or =4 days).', 'The prevalence of obesity in the surgical intensive care unit was 26.7%; extreme obesity was observed in 6.8%. In the full cohort of patients (n = 1373), median length of stay was short (2 days) and there were no differences in mortality in patients among any of the body mass index classes. In the subgroup of prolonged stay patients (n = 406), intensive care unit and hospital mortality rates were significantly increased in extremely obese patients compared with all other patients (intensive care unit, 33.3% vs. 12.3%, p = .009; hospital, 33.3% vs. 16%, p = .045). Multivariate analysis showed that extreme obesity was an independent predictor of death in surgical critically ill patients with prolonged intensive care unit stay after controlling for age, gender, and severity of illness. The odds of death increased 7.4 times in patients with morbid obesity.'] Is morbid obesity an independent determinant of death among surgical critically ill patients?