The APACHE II and TISS scales usually are used in intensive medicine services to assess patient's severity and therapeutic requirements, respectively. Both scales serve to classify ICU patient's into three care levels, each of which has its own well-defined surveillance and care requirements. Nursing personnel have used the TISS scale to determine work loads and plan nurse-patient ratios. However, this scale is complex and its application is time-consuming, thus impeding its routine use. In recent years, the NEMS (Nine Equivalents of Nursing Manpower) scale has been validated for this purpose. This scale uses just nine variables to objectively quantify nursing requirements. In order to determine if the NEMS scale could be used to evaluate the severity and nursing requirements of patient's admitted to our ICU and to establish care levels, we designed a descriptive study of a sample of 78 patients. The results showed that the APACHE II, TISS and NEMS scales has a good correlation and that the NEMS scale could be used to determine patient care requirements in our service. Based on the TISS and NEMS correlation, we determined discriminative numerical NEMS values for assigning patient's to different care levels.