The introduction of ICD-10 has changed the diagnostic borders of affective disorders in clinical psychiatry. The current study presents the diagnostic concordance between ICD-8 diagnoses given in 1993 and ICD-10 diagnoses given in 1994 to the same patients admitted in both years, according to the Danish register of psychiatric admissions. In total, 1,487 patients received an ICD-8 diagnosis of manic-depressive psychoses in 1993 and were re-admitted in 1994. The majority of patients (84.0%) with a manic-depressive diagnosis according to ICD-8 received a diagnosis of affective disorder according to ICD-10. Patients with a diagnosis of affective disorder according to ICD-10 had previously been diagnosed as manic-depressive (69.6%), psychogenic psychoses (8.7%), personality disorders (5.5%) or neurosis (3.2%) according to ICD-8. The ICD-10 concept of affective disorder thus appeared broader and more comprehensive compared with ICD-8.