In this paper, we present a model for conceptualizing the etiology of boyhood gender identity disorder. We illustrate the model with a specific case of a three-year-old boy who developed a gender identity disorder in reaction to his mother's depression after she had an abortion. We describe how the temperament of the child, his reaction to a psychic trauma during a sensitive period of mental representational development, and multigenerational transmission of psychodynamics lead to a gender identity disorder. We view the cross-gender fantasy as a compromise formation for the management of separation anxiety and aggression, and we view its enactment in behavior, in part, as a defensive attempt to understand an unmetabolizable experience of aggression. This case offers an unusual window into understanding how interpersonal experience, particularly in the face of severe anxiety, becomes transformed into intrapsychic phenomena and how pathological beliefs both encode experience and construct psychic reality.