OBJECTIVE The objectives of the study were to identify the daily nursing workload in an intensive care unit (ICU) and to analyse the adequacy of nursing staff in a six hour shift according to the Nursing Activities Score (NAS). METHODS The sample consisted of 68 patients from a general 25-bed adult ICU in a private hospital with 250 beds in São Paulo, Brazil. The nursing workload of all patients admitted in the ICU over a one month period in 2004 were measured daily according to the NAS. For the analysis of nursing staff it was considered the number of nurses available in a six hour shift. Data were submitted to descriptive analyses. RESULTS Most patients were elderly and remained on average 12 (+/-16.4) days in the ICU. The mean NAS was 63.7 (+/-2.4%) and remained above 58.5% throughout the month. Apart from the 16th day of data collection there was an excess of nursing professionals in a six hour shift during the study period (range from 0.8 to 4.8 professionals). CONCLUSIONS The study results show the importance of nursing staff adequacy to workload fluctuations for reducing ICU costs.