Noticed is that the ICD-9-CM as a classification system has many shortcomings. Several are described. To calculate the diagnostic reliability with ICD-9-CM, a simple method with correction for chance is described and employed. Six residents and one psychiatrist chose categories with twenty standardised discharge-letters. A Kappa-coefficient of reliability of .37 was found. After comparison with previous research the authors suggest that with ICD-9-CM classification no acceptable diagnostic reliability could be achieved. The authors recommend that the ICD-9-CM for the tentral registration of psychiatrie diseases in the Netherlands, be replaced when research in this country confirms a better reliability of DSM-III.