IntroductionMental disorders are common among prison inmates, with a high rate of recidivism found among those with severe mental disorders. In Japan, the number of inmates with mental disorders has been increasing with the increasing rate of recidivism. Prisoners need an uninterrupted connection to post-release support to prevent them from being incarcerated again. This study identified inmates diagnosed with mental disorders whose recidivism had recently increased to investigate recidivism among inmates with severe mental disorders and the risk factors for reincarceration. MethodsThis study included 148 prisoners released from the Medical Correction Center in East Japan. Clinical diagnoses were coded using the World Health Organization's International Classification of Diseases, Tenth Revision. Risk factors focusing on the central eight items were categorized, and recidivism within 3 years of release was investigated. ResultOverall, the recidivism rate was 29.7%, with the risk of recidivism increasing by 170% in inmates with multiple incarcerations. A diagnosis of intellectual disability increased the risk of recidivism by 176%. Patients with schizophrenia were consistently less likely to recidivate than patients with other disorders. ConclusionIntellectual disability was identified as a risk factor for recidivism, as was multiple incarcerations. These prisoners may not be connected to medical and social services and thus may not be receiving appropriate assistance. Patients with schizophrenia might be more likely to be connected to medical care and receive support after release. Further research should be conducted using these findings to prevent recidivism among inmates with mental disorders.