BACKGROUND: Our main outcome was to identify organizational characteristics that help to evaluate the differences between the intensive care mortality ratios adjusted by APACHE II. We incorporated the variation associated with the ranking of institutions simulating its random effects under a binomial distribution. METHODS: A nationwide survey on structure, technology, and staffing resources available in Colombian intensive care units during 1997-1998 was conducted. We collected data on admissions from 20 randomly selected adult medical and surgical intensive care units. RESULTS: The mortality ratio from the 20 intensive care units ranged from 0.59 to 2.36; 80% of the intensive care units had a mortality ratio greater than 1. All four intensive care units with the lowest mortality ratio belonged to private institutions, while four of five institutions with the highest mortality belonged to the public sector. Intensive care units in private institutions also had fewer number of beds, lower median length of stay, lower occupancy rates, higher education training for specialists and nurses and fewer emergency nonelective surgical procedures. CONCLUSION: We successfully accounted for intensive care mortality baseline differences and random effects variations. There were substantial differences between intensive care units in institution type, bed availability, technology, staffing resources, and degree of training, which may have been associated with patient outcome. These results are of crucial importance to track, detect and assess future changes.