With introduction of ICD-10 from 1992 in WHO-memberstates there will be considerable change in psychiatric diagnoses. It is the first time that an operational diagnostic approach is introduced in psychiatric routine with a WHO-classification system. Following a historical overview basic concepts of ICD-10 and the most important innovations are demonstrated in view of the results of field trials. The new classification was widely accepted during the first tests, reliability of diagnosis could be improved. It should not be overlooked that in spite of methodological perfection many problems regarding content still have to be solved.