Legal sterilization has been applied to 269 mental defectives in S. Dakota. Incomplete family histories show 278 mental defectives, 64 borderline, 21 insane and 16 epileptics among relatives. The patients already have 5.8 siblings per patient and some of the parents are still of child bearing age. Only 11 out of 100 "sex offenders" have repeated since sterilization. The more complete family histories indicate the difficulty of social control, by sterilization, due to the multiple recessive character of mental de-fectiveness. However, reduction of mental defectiveness'' in families by rigid application of compulsory sterilization has been demonstrated.