This paper examines the proposition that the incidence of child sexual abuse by female perpetrators is underestimated. This may be due to a culturally based unwillingness to believe that women commit such acts. Female sexual offenders have been little studied and poorly understood. Until recently mother-child incest was considered to be virtually nonexistant and there remains a huge discrepancy in the incidence of male and female offenders. The predisposing factors contributing to this situation are examined for both men and women and an illustrative case history of mother-son incest is used to highlight our prejudices. The tentative conclusions reached are that (1) we underestimate the incidence of sexual abuse of male and female children by women and that (2) the changing roles of men and women in Western societies may lead to an increase in such abuse.