This study is the first part in a series of the articles reporting results of a project conducted to analyse the structural resources of ICUs in São Paulo city. This article describes the characteristics of those Units, considering the quantity and geographic location, bed number, maintainer entity, type of assistance, type of client, as well the percentage of beds usage and length of stay. Forty three ICUs were analysed and a questionnaire answered by the ICU nurse coordinator was used to collect data. The results showed that the number of ICUs in the hospital varied from 1 to 4, being more frequently those with only one ICU (68.8%). 79.2% of the Units were in private hospitals, located in the central area of the city. ICU beds represented 8.0% of the total hospital beds and there was an average of 10 beds per Unit. There was a predominance of general ICUs (60.5%), destined only for adult patients (51.2%) and for clinical-surgical treatment (95.3%). The percentage of beds usage in majority of ICU was between 80 to 100% and the length of stay was 4,5 days.