Background: Client categorization is a management tool that allows an objective and structured assessment of the care demands imposed by patients and nursing workloads. Aim: To characterize the need for direct nursing care of patients admitted to a university hospital. Patients and methods: During two months, all patients admitted to intensive, intermediate care units and general services were categorized, their need for nursing care and the time invested by nurses in their care was registered. All patients were classified as maximal, high, median or low risk and as independent, totally or partially dependent on nursing care. Considering four degrees of risk and three degrees of dependency, 12 categories of patients were defined. Results: Patients admitted to intensive care units were of maximal risk and totally dependent and required 1 nurse per 2.2 patients. Those admitted in intermediate care units required 1 nurse per 3.8 patients and those in general services, 1 nurse per 11.5 patients. Conclusions: Client categorization is a reproducible method that determines a standard measuring unit to define nursing needs. This allows the comparison of workloads between different services within a hospital or between hospitals