Most psychoanalytic literature dealing with incest holds the premise that the act took place between a parent and a child of opposite sex. Incidentally, most of these cases involve a father-daughter incest (e.g. research by Julien Bigras). However, this is only one of four mathematically possible combinations. For instance, we tend to underestimate the occurrences and, consequently, the repercussions of mother-daughter incest relationships. The biological and psychological importance of the mother in the child's