The measurement of nursing workload first began in the 1970s, because of the need for determining severity of illness and cost-effectiveness in the intensive care unit. In the following decades, the need for more specific tools for assessing nursing workload brought to the development of scoring systems more focused on nursing activities. We will briefly review the scoring systems validated since 1974. TISS-Therapeutic Intervention Scoring System elaborated by Cullen in 1974 is based on 57 therapeutic procedures and was designed to assess the severity of illness in the ICU. Each intervention scores 1 to 4. Patients are grouped in 5 classes. It was not sufficiently validated and was abandoned. However it first introduced the idea of "patient point managed per nurse". TISS update was elaborated by Keene in 1983. The therapeutic procedures were increased to 76. It was assumed that a single nurse can manage 40/50 points per day. Though not validated, it became the most used tool to assess complexity of treatment and nurse/patient ratio. However many of these items are obsolete and frequently related to the severity of illness rather than to specific nursing interventions. PRN-Project Research of Nursing was elaborated by EROS during 1980-1987. Points are assigned to each nursing activity according to their frequency, duration, need for more than one nurse, etc. It results quite time consuming, thus unsuitable for routine use. OMEGA elaborated in 1986 describes 86 therapeutic interventions, grouped in 3 categories, measured at the end of ICU stay, thus representing a measure of global workload and use of resources. TOSS-Time Oriented Score System was elaborated by GIRTI in 1991. This score was studied and tested in Italy. It represents a direct temporal evaluation of nursing workload. The score is expressed in minutes. It is reliable and relatively simple, and has been validated on over 2 700 ICU patients. TISS 28 was elaborated by Miranda in 1996. It represents a simplified and updated version of the original TISS, proposed to assess the nursing workload. The authors stated that a nurse can deal with 46 points over the 24 hours. NEMS-Nine Equivalents of nursing Manpower use Score was elaborated by Miranda in 1997. It was derived from TISS and TISS28. Only 9 items, related to specific organ support, nursing and diagnostic/therapeutic interventions inside or outside the ICU, are considered. These items were weighted by multivariate analysis, obtaining a score comparable to the TISS28 score. Each nurse can deal with 45/50 points per day. NAS-Nursing Activity Score was elaborated by Miranda in 2003. It was derived from TISS28, aiming at the description of nursing activities not necessarily correlated to the severity of illness. It describes 81% of the nursing time, compared to 43% of TISS 28. In conclusion, many scoring systems have been proposed to describe nursing workload, both directly (as with TOSS and PRN) or through severity and complexity of treatment (TISS, TISS 28, NAS and NEMS). These scores represent the instruments to assess the correct use of ICU resources.