Medical institutions unjustifiably 'walk in a fog of misplaced optimism', convinced of the accuracy of clinical diagnosis. They disregard the fact that the latest diagnostic research has not reduced the frequency of diagnostic inaccuracy. We reviewed the autopsy records from the archive of the Institute of Forensic Medicine of 921 decreased persons in 1997 and compared the clinical with the post-mortem diagnoses. Group 1 included cases of complete agreement between the clinical and post-mortem diagnoses, Group 2 cases of partial disagreement about the direct cause of death, Group 3 cases of disagreement about the basic illness, Group 4 cases of total disagreement between the clinical diagnosis and the post-mortem. Group 5 included cases of improper filling out of documentation according to the ABC international classification of diseases, injuries and causes of death, which has been accepted by the World Health Organisation in 10 revisions to date (WHO, 1992). The diagnoses were in total agreement in 48.87% of the cases, in partial agreement (disagreement about the direct cause of death) in 22.74%, and in disagreement about the basic illness in 13.5%. Of the cases, 9.68% were classified into Group 5.