The relative contributions of mental illness and substance use disorders to criminal recidivism have important clinical and policy implications. This study reviewed 36 months of postrelease data for nearly 10,000 New Jersey state inmates released in 2013 to ascertain the rearrest rate of those diagnosed with mental illness, substance use disorders, both, or neither. We also examined whether certain characteristics suggestive of higher risk of psychiatric decompensation were associated with higher rates of rearrest. Released inmates who were diagnosed with a substance use disorder (without a mental illness) while incarcerated had the highest rate of rearrest upon release, followed by inmates diagnosed with both mental illness and substance use disorder together, inmates with neither a substance use disorder nor a mental illness, and lastly by inmates diagnosed with mental illness alone. These differences were statistically significant only between inmates with substance use disorders and those without a substance use disorder. Among those with a diagnosed mental disorder, there were no statistically significant differences in recidivism based on diagnosis or based on prescription of antipsychotic medication, injectable antipsychotic medication, or involuntary antipsychotic medication. These results support correctional institutions assertively addressing substance use disorders, especially for individuals returning to the community.