Filicide is a form of family violence in which a child is killed by his or her own parent. Most of the literature on filicide addresses the association of mental illness, motivation, and other risk factors with the perpetration of filicide. However, almost no research has addressed the intellectual functioning of perpetrators. We investigated intellectual functioning in a collection of forensic cases seen by the first author over an eight-year period. Nineteen patients who underwent forensic psychiatric evaluation for filicide from August of 1993 to April of 2001 were studied using retrospective case review methodology. Data were obtained from medical and forensic records, reports of family members, legal documents, and other collateral sources. We found that mental illness is common among perpetrators, supporting other findings in the literature. In addition, we found a high frequency of substance abuse among parents who killed their children. However, we also found a significant frequency of intellectual impairment and argue that this factor may have been overlooked in the history of filicide investigations. Familial psychodynamics of filicide will be reviewed and discussed.