Background: Psychiatric inpatient registers are often used in research in the Nordic countries. We aimed to investigate the validity of recorded diagnoses of schizophrenia in the Swedish National Inpatient Register, in cases of early age at onset. We also wanted to describe the accuracy of the diagnoses in cities/university clinics and country hospitals as well as in child and adolescent psychiatric clinics and clinics for adults.
Method: One hundred cases with a diagnosis of schizophrenia, born 1973-1977, were randomly selected. The psychiatric records were scrutinised according to the criteria of DSM-IV.
Results: Eighty-six per cent (95 % CI 78-93 %) fulfilled the DSM-IV criteria of schizophrenia syndrome and 76 % (95 % CI 66-86 %) fulfilled the "narrow" definition. There were no large differences in the accuracy of the diagnoses between regions or clinics.
Conclusion: The proportion of "true" cases of schizophrenia is high in the Swedish National Inpatient Register. In addition, the results did not support large differences between clinics or regions although a larger sample size would be needed to test this formally. In comparison with earlier studies from the Nordic countries the validity seems to be quite stable over time, between different ages at onset and between Nordic countries. Thus, the registers are well suited to be used in schizophrenia research.