This article reviews psychoanalytic theory, clinical studies, and empirical investigations regarding the pathological effects of father-daughter incest. This literature suggests strong links between childhood incest and serious psychopathological sequelae, particularly borderline personality disorder. I propose a model for understanding the impact of incest, using the concept of identity as a mediating construct. Particular emphasis is placed on the role played by incest in the disruption of the developing boundary between internal and external reality. Such defects may result in the failure of age-appropriate divestment of the illusion of omnipotent control and the inappropriate persistence of efforts to control others. Thus, such disruptions may account for major aspects of borderline syndrome including identity diffusion, affective instability, and primitive defenses. A case vignette is presented as an illustration of the model's cogency with respect to the treatment of a borderline incest victim. Theoretical, treatment, and research implications are noted.