The reliability of psychiatric diagnoses was assessed making use of data from a centralized registration of patients in psychiatric hospitals. One major conclusion is that about 80% of the patients is given the same diagnosis at admission as upon release. When readmitted to the same hospital within one year, approximately 60% was given a diagnosis in accordance with the diagnosis at the time of their previous discharge. When readmitted to another hospital, the reliability drops to 45%. These results are analysed and some conclusions regarding the causes of the measure of agreement are drawn.