It is not unreasonable to expect that some biological predisposition toward antisocial behavior may characterize the most serious of recidivistic and violent criminal offenders. This study used the adoption method to examine the contribution of mental disorder in adoptees' biological backgrounds to their recidivistic and violent criminal offending. Multiple recidivistic nonviolent criminal behavior was found at a significantly elevated rate in adopted-away sons when mental disorder and criminal involvement were characteristic of the adoptees' biological families. A similar, but nonsignificant, elevation was found for rates of violence. Parental diagnostic types associated most strongly with sons' later criminal involvement were drug abuse, alcohol abuse, and personality disorders. Parental psychoses were not related to offspring recidivism or violence in this cohort. Possible confounding effects of missing data, institutionalization prior to adoption, information given to adoptive parents by the adoption agencies about the child's biological background, historical period, perinatal factors, and selective placement were considered. Perinatal factors could not be discounted as contributors to the findings.