A prospective study of 100 autopsies was carried out. The clinical and pathologic diagnoses were made independently by intensivists and pathologists; at the end of the study, the differences were determined. There were seven Class I errors (which if detected before death, would probably have led to a change in management that might have resulted in cure or prolonged survival), six of these relating to the basic disease and one to the cause of death. Class II errors occurred in 15 patients, ten relating to the basic disease and five to the cause of death. In 61% of the patients, the major and minor diagnoses coincided. In 77% of the patients, the major diagnoses coincided. No relationship was found between the incidence of Class I and Class II errors and the length of the patients' stay in the ICU.