Aggressive and disruptive behaviors often precede the onset of schizophrenia. In this register-based follow-up study with a case-control design, we wanted to investigate if serious delinquency was associated with future diagnoses of schizophrenia or schizoaffective disorder (here, broadly defined schizophrenia) among a nationwide consecutive sample of 15- to 19-year-old Finnish delinquents sent for a forensic psychiatric examination in 1989–2010.

The sample comprised 313 delinquents with no past or current psychotic disorder. For each delinquent, four age-, gender- and place of birth -matched controls were randomly selected from the Central Population Register. Five controls (0.4%) had been treated for schizophrenia before their respective index-dates and were thus excluded from further analysis, leaving us with a control population of 1247 individuals. The subjects were followed till death, emigration or the end of 2015, whichever occurred first. Diagnoses were obtained from the Care Register for Health Care.

Forty (12.8%) of the delinquents and 11 (0.9%) of the controls were diagnosed with schizophrenia later in life (HR 16.6, 95% CI 8.53–32.39, P<0.001). Almost half of the pretrial adolescents with later schizophrenia were diagnosed within 5years of the forensic psychiatric examination, but latency was longer among the other half of the sample, reaching up to 20.5years.

The study supports the previous research indicating a potential link between serious delinquency and later schizophrenia. Accurate psychiatric assessments should be made in correctional services but also later in life so that any possible psychotic symptoms can be detected in individuals with a history of serious delinquency even if there were no signs of psychosis before or at the time of the crime. Future research should explore which factors influence the delinquent's risk of developing later schizophrenia.