Development of serious mental illness in young adult violent offenders: Early-life risk factors and long-term adverse outcomes

• Ten percent of imprisoned young violent offenders had a history of severe mental illness. • Childhood-onset conduct disorder emerged as a key early-life risk factor. • Severe mental illness was prospectively linked to higher reconviction rates and increased psychiatric inpatient care but limited outpatient care use. • Targeted interventions needed during incarceration and post-release reintegration. This study explored serious mental illness (SMI) in young adult offenders imprisoned for violent or sexual crimes, estimating the effects of neurodevelopmental disorders and early-life risk factors on the development of SMI, and its prospective long-term adverse outcomes. An all-male cohort of 266 violent offenders, assessed during imprisonment when aged 18–25 years (M = 21.8, SD = 1.9), was followed prospectively ( M years = 6.2, SD = 1.3) in Swedish national registers together with a general population group ( n = 10,000). The baseline prevalence of SMI in late adolescence or young adulthood was 10 % ( n = 26) in the violent offender cohort. Childhood-onset conduct disorder (OR 2.7 1.0–7.1) was associated with SMI in multivariable logistic regression analyses. Prospectively, violent offenders with, versus without, SMI exhibited heightened total crime rate (IRR 1.4 1.0–2.2), prison reconvictions (IRR 1.5 1.0–2.1), and psychiatric inpatient care (IRR 3.7 1.6–8.4), in zero-inflated Poisson regression models. The usage of outpatient psychiatric and somatic care was low in violent offenders with SMI, even relative to the general population group. The results emphasize the need for early identification of at-risk children, such as those with childhood-onset conduct disorder, and challenges with engaging violent offenders with SMI in healthcare.