Patients admitted to intensive care units (ICU) experience constant changes in their general condition. Therefore, the determination of Apache score within the first 24 hours of admission may not be a reliable index of severity. The aim of this study was to measure daily Apache scores in ICU patients, and to determine if the maximum score (Maximum Apache) attained during hospitalization had a better prognostic value than that of admission. We measured daily Apache scores to 314 patients admitted to Hospital Clinico UC ICU. Mean admission score was 17.5 +/- 9.3 (range: 1-47) and mean maximum score was 18.6 +/- 9.7 (range: 1-47), p < 0.001. Mortality during ICU stay was 17.2%, and 8.6% during hospitalization after ICU discharge. Only 78.3% of patients attained their maximum apache score during the first 24 hours of admission, whereas 21.7% attained it during the rest of ICU hospitalization. Excluding subjects with less than one day of ICU stay, 33% of patients attained maximum Apache score after 24 hours of ICU admission. Statistical analysis showed that maximum Apache score was a better predictor of mortality than that of admission.