OBJECTIVE The aim of this study was to analyze the morbidity and the mortality of critically ill patients admitted to the intensive care unit in a teaching hospital, using the APACHE II score. METHODS Descriptive and retrospective study, with analysis of 300 patients admitted to ICU from March 2004 to July 2005. RESULTS Of the 300 patients admitted to ICU, 51.7% were men, average 54.2 ± 19.57 years and 78% from the wards of the teaching hospital itself. There was more prevalence of patients aged 60 years or older (43%). The main dysfunctions were from the respiratory and cardiocirculatory systems. Length of stay in ICU was 7.51 ± 8.21 days. The mean of APACHE II was 16.48 ± 7.67, with meaningful difference between survivors and deceased patients. The real mortality rate in ICU was 32.7%, without meaningful difference between patients that died before or after 48 hours. The standardized mortality ratio was 1.1. CONCLUSIONS Despite the severity of the patients admitted to ICU, the standardized mortality ratio suggests a satisfactory quality in the service.