Just as childhood incest is underreported, so is sibling incest. It occurs far more frequently than many want to believe although many of the same reasons for father-daughter incest (the most prominent) are the same. In fact, sibling incest is estimated to occur 3-5 times as often as father-daughter incest. Once again, the root causes lie with faulty/uninformed parenting skills.
For abuse to occur, perpetrators have to have access to children. Who has the most access? Parents and siblings. And, when the parents are:
- Demonstrate poor boundaries,
- Provide little or no direction on conflict resolution skills, and
- Model unhealthy behavior,
the smallest and most vulnerable pay the price. The younger siblings have to fend for themselves with no direction.
Sibling assault can be defined as “a repeated pattern of aggression directed toward a sibling with the intent to inflict harm, and motivated by an internal emotional need for power and control. When siblings are close in age, the typical excuses for aggression toward each other are that younger children normally get involved in harmless sex play or that sibling fighting is normal family behavior. In my article Sibling Incest, I provide more in depth descriptions of this behavior.
Three family configurations are commonly found in sibling abuse families:
- Peripheral parent families: One parent is absent a lot and abusive when s/he reenters the household. Children’s needs for love, attention, and support are not met, so they turn toward each other. Since their interactions are not often supervised and the children have not been taught appropriate behavior, sibling incest can occur—especially when an older sibling feels resentful and aggressive.
- Pseudo-consensual sibling incest families: When the home is sexually charged and there is ongoing parental abuse or neglect, siblings many times turn toward each other to get the emotional support not provided by the parents.
- Pseudo-parent sibling families: When neither parent is available, many times the oldest child is positioned as the caretaker to his/her siblings. With the older sibling in charge and s/he has had no modeling provided by the parents for healthy behavior, when s/he becomes sexually aware, s/he may relate to younger siblings erotically.
All three of these examples show how the physical and psychological abandonment by the parents can lead to abusive behavior, and consequently, long-term harmful effects for their children.
 “Sibling incest: The myth of benign sibling incest,” E. Cole, Women and Therapy, 5, 79-89, (1982); “Sibling incest: A study of the dynamics of 25 cases,” H. Smith & E. Israel, Child Abuse & Neglect, 11, 101-108, (1987).
 “Treating sibling abuse families,” John V. Caffaro, Allison Conn-Caffaro, Aggression and Violent Behavior 10, 604-623, (2005).